diff --git a/agb/Cargo.lock b/agb/Cargo.lock
index 88f57060..a7a46153 100644
--- a/agb/Cargo.lock
+++ b/agb/Cargo.lock
@@ -16,6 +16,7 @@ dependencies = [
  "agb_image_converter",
  "agb_macros",
  "agb_sound_converter",
+ "bare-metal",
  "bitflags",
 ]
 
@@ -64,6 +65,12 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
+[[package]]
+name = "bare-metal"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8fe8f5a8a398345e52358e18ff07cc17a568fbca5c6f73873d3a62056309603"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
diff --git a/agb/Cargo.toml b/agb/Cargo.toml
index 627bfc96..dbd7d298 100644
--- a/agb/Cargo.toml
+++ b/agb/Cargo.toml
@@ -25,6 +25,7 @@ agb_image_converter = { version = "0.6.0", path = "../agb-image-converter" }
 agb_sound_converter = { version = "0.1.0", path = "../agb-sound-converter" }
 agb_macros = { version = "0.1.0", path = "../agb-macros" }
 agb_fixnum = { version = "0.1.0", path = "../agb-fixnum" }
+bare-metal = "1.0"
 
 [package.metadata.docs.rs]
 default-target = "thumbv6m-none-eabi"
diff --git a/agb/examples/output.rs b/agb/examples/output.rs
index 85e9cf65..e28558f6 100644
--- a/agb/examples/output.rs
+++ b/agb/examples/output.rs
@@ -1,13 +1,20 @@
 #![no_std]
 #![no_main]
 
+use core::cell::RefCell;
+
+use bare_metal::{CriticalSection, Mutex};
+
 #[agb::entry]
 fn main(_gba: agb::Gba) -> ! {
-    let count = agb::interrupt::Mutex::new(0);
-    agb::add_interrupt_handler!(agb::interrupt::Interrupt::VBlank, |key| {
-        let mut count = count.lock_with_key(&key);
-        agb::println!("Hello, world, frame = {}", *count);
-        *count += 1;
-    });
+    let count = Mutex::new(RefCell::new(0));
+    agb::add_interrupt_handler!(
+        agb::interrupt::Interrupt::VBlank,
+        |key: &CriticalSection| {
+            let mut count = count.borrow(*key).borrow_mut();
+            agb::println!("Hello, world, frame = {}", *count);
+            *count += 1;
+        }
+    );
     loop {}
 }
diff --git a/agb/examples/wave.rs b/agb/examples/wave.rs
index 79b11081..9036eb9a 100644
--- a/agb/examples/wave.rs
+++ b/agb/examples/wave.rs
@@ -1,11 +1,14 @@
 #![no_std]
 #![no_main]
 
+use core::cell::RefCell;
+
 use agb::{
     display::example_logo,
     fixnum::FixedNum,
-    interrupt::{Interrupt, Mutex},
+    interrupt::{free, Interrupt},
 };
+use bare_metal::{CriticalSection, Mutex};
 
 struct BackCosines {
     cosines: [u16; 32],
@@ -21,10 +24,10 @@ fn main(mut gba: agb::Gba) -> ! {
     let mut time = 0;
     let cosines = [0_u16; 32];
 
-    let back = Mutex::new(BackCosines { cosines, row: 0 });
+    let back = Mutex::new(RefCell::new(BackCosines { cosines, row: 0 }));
 
-    agb::add_interrupt_handler!(Interrupt::HBlank, |_| {
-        let mut backc = back.lock();
+    agb::add_interrupt_handler!(Interrupt::HBlank, |key: &CriticalSection| {
+        let mut backc = back.borrow(*key).borrow_mut();
         let deflection = backc.cosines[backc.row % 32];
         unsafe { ((0x0400_0010) as *mut u16).write_volatile(deflection) }
         backc.row += 1;
@@ -34,14 +37,17 @@ fn main(mut gba: agb::Gba) -> ! {
 
     loop {
         vblank.wait_for_vblank();
-        let mut backc = back.lock();
-        backc.row = 0;
-        time += 1;
-        for (r, a) in backc.cosines.iter_mut().enumerate() {
-            let n: FixedNum<8> = (FixedNum::new(r as i32) / 32 + FixedNum::new(time) / 128).cos()
-                * (256 * 4 - 1)
-                / 256;
-            *a = (n.trunc() % (32 * 8)) as u16;
-        }
+        free(|key| {
+            let mut backc = back.borrow(*key).borrow_mut();
+            backc.row = 0;
+            time += 1;
+            for (r, a) in backc.cosines.iter_mut().enumerate() {
+                let n: FixedNum<8> = (FixedNum::new(r as i32) / 32 + FixedNum::new(time) / 128)
+                    .cos()
+                    * (256 * 4 - 1)
+                    / 256;
+                *a = (n.trunc() % (32 * 8)) as u16;
+            }
+        })
     }
 }
diff --git a/agb/src/agb_alloc/block_allocator.rs b/agb/src/agb_alloc/block_allocator.rs
index 6ca3108c..6dfb154b 100644
--- a/agb/src/agb_alloc/block_allocator.rs
+++ b/agb/src/agb_alloc/block_allocator.rs
@@ -1,16 +1,28 @@
+//! The block allocator works by maintaining a linked list of unused blocks and
+//! requesting new blocks using a bump allocator. Freed blocks are inserted into
+//! the linked list in order of pointer. Blocks are then merged after every
+//! free.
+
 use core::alloc::{GlobalAlloc, Layout};
+
+use core::cell::RefCell;
+use core::convert::TryInto;
 use core::ptr::NonNull;
 
-use crate::interrupt::Mutex;
+use crate::interrupt::free;
+use bare_metal::{CriticalSection, Mutex};
 
 use super::bump_allocator::BumpAllocator;
+use super::SendNonNull;
 
 struct Block {
     size: usize,
-    next: Option<NonNull<Block>>,
+    next: Option<SendNonNull<Block>>,
 }
 
 impl Block {
+    /// Returns the layout of either the block or the wanted layout aligned to
+    /// the maximum alignment used (double word).
     pub fn either_layout(layout: Layout) -> Layout {
         let block_layout = Layout::new::<Block>();
         let aligned_to = layout
@@ -21,31 +33,83 @@ impl Block {
             aligned_to.align(),
         )
         .expect("too large allocation")
+        .align_to(8)
+        .expect("too large allocation")
+        .pad_to_align()
     }
 }
 
 struct BlockAllocatorState {
-    first_free_block: Option<NonNull<Block>>,
+    first_free_block: Option<SendNonNull<Block>>,
 }
 
 pub(crate) struct BlockAllocator {
     inner_allocator: BumpAllocator,
-    state: Mutex<BlockAllocatorState>,
+    state: Mutex<RefCell<BlockAllocatorState>>,
 }
 
 impl BlockAllocator {
     pub(super) const unsafe fn new() -> Self {
         Self {
             inner_allocator: BumpAllocator::new(),
-            state: Mutex::new(BlockAllocatorState {
+            state: Mutex::new(RefCell::new(BlockAllocatorState {
                 first_free_block: None,
-            }),
+            })),
         }
     }
 
-    unsafe fn new_block(&self, layout: Layout) -> *mut u8 {
+    #[cfg(test)]
+    pub unsafe fn number_of_blocks(&self) -> u32 {
+        free(|key| {
+            let mut state = self.state.borrow(*key).borrow_mut();
+
+            let mut count = 0;
+
+            let mut list_ptr = &mut state.first_free_block;
+            while let Some(mut curr) = list_ptr {
+                count += 1;
+                list_ptr = &mut curr.as_mut().next;
+            }
+
+            count
+        })
+    }
+
+    /// Requests a brand new block from the inner bump allocator
+    fn new_block(&self, layout: Layout, cs: &CriticalSection) -> *mut u8 {
         let overall_layout = Block::either_layout(layout);
-        self.inner_allocator.alloc(overall_layout)
+        self.inner_allocator.alloc_critical(overall_layout, cs)
+    }
+
+    /// Merges blocks together to create a normalised list
+    unsafe fn normalise(&self) {
+        free(|key| {
+            let mut state = self.state.borrow(*key).borrow_mut();
+
+            let mut list_ptr = &mut state.first_free_block;
+
+            while let Some(mut curr) = list_ptr {
+                if let Some(next_elem) = curr.as_mut().next {
+                    let difference = next_elem
+                        .as_ptr()
+                        .cast::<u8>()
+                        .offset_from(curr.as_ptr().cast::<u8>());
+                    let usize_difference: usize = difference
+                        .try_into()
+                        .expect("distances in alloc'd blocks must be positive");
+
+                    if usize_difference == curr.as_mut().size {
+                        let current = curr.as_mut();
+                        let next = next_elem.as_ref();
+
+                        current.size += next.size;
+                        current.next = next.next;
+                        continue;
+                    }
+                }
+                list_ptr = &mut curr.as_mut().next;
+            }
+        });
     }
 }
 
@@ -54,13 +118,17 @@ unsafe impl GlobalAlloc for BlockAllocator {
         // find a block that this current request fits in
         let full_layout = Block::either_layout(layout);
 
-        let (block_after_layout, block_after_layout_offset) =
-            full_layout.extend(Layout::new::<Block>()).unwrap();
+        let (block_after_layout, block_after_layout_offset) = full_layout
+            .extend(Layout::new::<Block>().align_to(8).unwrap().pad_to_align())
+            .unwrap();
 
-        {
-            let mut state = self.state.lock();
+        free(|key| {
+            let mut state = self.state.borrow(*key).borrow_mut();
             let mut current_block = state.first_free_block;
             let mut list_ptr = &mut state.first_free_block;
+            // This iterates the free list until it either finds a block that
+            // is the exact size requested or a block that can be split into
+            // one with the desired size and another block header.
             while let Some(mut curr) = current_block {
                 let curr_block = curr.as_mut();
                 if curr_block.size == full_layout.size() {
@@ -78,26 +146,57 @@ unsafe impl GlobalAlloc for BlockAllocator {
                         .add(block_after_layout_offset)
                         .cast();
                     *split_ptr = split_block;
-                    *list_ptr = NonNull::new(split_ptr);
+                    *list_ptr = NonNull::new(split_ptr).map(SendNonNull);
 
                     return curr.as_ptr().cast();
                 }
                 current_block = curr_block.next;
                 list_ptr = &mut curr_block.next;
             }
-        }
 
-        self.new_block(layout)
+            self.new_block(layout, key)
+        })
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        let new_layout = Block::either_layout(layout);
-        let mut state = self.state.lock();
-        let new_block_content = Block {
-            size: new_layout.size(),
-            next: state.first_free_block,
-        };
-        *ptr.cast() = new_block_content;
-        state.first_free_block = NonNull::new(ptr.cast());
+        let new_layout = Block::either_layout(layout).pad_to_align();
+        free(|key| {
+            let mut state = self.state.borrow(*key).borrow_mut();
+
+            // note that this is a reference to a pointer
+            let mut list_ptr = &mut state.first_free_block;
+
+            // This searches the free list until it finds a block further along
+            // than the block that is being freed. The newly freed block is then
+            // inserted before this block. If the end of the list is reached
+            // then the block is placed at the end with no new block after it.
+            loop {
+                match list_ptr {
+                    Some(mut current_block) => {
+                        if current_block.as_ptr().cast() > ptr {
+                            let new_block_content = Block {
+                                size: new_layout.size(),
+                                next: Some(current_block),
+                            };
+                            *ptr.cast() = new_block_content;
+                            *list_ptr = NonNull::new(ptr.cast()).map(SendNonNull);
+                            break;
+                        }
+                        list_ptr = &mut current_block.as_mut().next;
+                    }
+                    None => {
+                        // reached the end of the list without finding a place to insert the value
+                        let new_block_content = Block {
+                            size: new_layout.size(),
+                            next: None,
+                        };
+                        *ptr.cast() = new_block_content;
+                        *list_ptr = NonNull::new(ptr.cast()).map(SendNonNull);
+                        break;
+                    }
+                }
+            }
+        });
+        self.normalise();
     }
 }
diff --git a/agb/src/agb_alloc/bump_allocator.rs b/agb/src/agb_alloc/bump_allocator.rs
index 1fe1ef8a..d1ddac3a 100644
--- a/agb/src/agb_alloc/bump_allocator.rs
+++ b/agb/src/agb_alloc/bump_allocator.rs
@@ -1,23 +1,26 @@
 use core::alloc::{GlobalAlloc, Layout};
+use core::cell::RefCell;
 use core::ptr::NonNull;
 
-use crate::interrupt::Mutex;
+use super::SendNonNull;
+use crate::interrupt::free;
+use bare_metal::{CriticalSection, Mutex};
 
 pub(crate) struct BumpAllocator {
-    current_ptr: Mutex<Option<NonNull<u8>>>,
+    current_ptr: Mutex<RefCell<Option<SendNonNull<u8>>>>,
 }
 
 impl BumpAllocator {
     pub const fn new() -> Self {
         Self {
-            current_ptr: Mutex::new(None),
+            current_ptr: Mutex::new(RefCell::new(None)),
         }
     }
 }
 
 impl BumpAllocator {
-    fn alloc_safe(&self, layout: Layout) -> *mut u8 {
-        let mut current_ptr = self.current_ptr.lock();
+    pub fn alloc_critical(&self, layout: Layout, cs: &CriticalSection) -> *mut u8 {
+        let mut current_ptr = self.current_ptr.borrow(*cs).borrow_mut();
 
         let ptr = if let Some(c) = *current_ptr {
             c.as_ptr() as usize
@@ -28,7 +31,7 @@ impl BumpAllocator {
         let alignment_bitmask = layout.align() - 1;
         let fixup = ptr & alignment_bitmask;
 
-        let amount_to_add = layout.align() - fixup;
+        let amount_to_add = (layout.align() - fixup) & alignment_bitmask;
 
         let resulting_ptr = ptr + amount_to_add;
         let new_current_ptr = resulting_ptr + layout.size();
@@ -37,10 +40,13 @@ impl BumpAllocator {
             return core::ptr::null_mut();
         }
 
-        *current_ptr = NonNull::new(new_current_ptr as *mut _);
+        *current_ptr = NonNull::new(new_current_ptr as *mut _).map(SendNonNull);
 
         resulting_ptr as *mut _
     }
+    pub fn alloc_safe(&self, layout: Layout) -> *mut u8 {
+        free(|key| self.alloc_critical(layout, key))
+    }
 }
 
 unsafe impl GlobalAlloc for BumpAllocator {
diff --git a/agb/src/agb_alloc/mod.rs b/agb/src/agb_alloc/mod.rs
index 9e9408f4..4084f3af 100644
--- a/agb/src/agb_alloc/mod.rs
+++ b/agb/src/agb_alloc/mod.rs
@@ -1,15 +1,45 @@
 use core::alloc::Layout;
+use core::ops::{Deref, DerefMut};
+use core::ptr::NonNull;
 
 mod block_allocator;
 mod bump_allocator;
 
 use block_allocator::BlockAllocator;
 
+struct SendNonNull<T>(NonNull<T>);
+unsafe impl<T> Send for SendNonNull<T> {}
+
+impl<T> Clone for SendNonNull<T> {
+    fn clone(&self) -> Self {
+        SendNonNull(self.0)
+    }
+}
+impl<T> Copy for SendNonNull<T> {}
+
+impl<T> Deref for SendNonNull<T> {
+    type Target = NonNull<T>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for SendNonNull<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
 const EWRAM_END: usize = 0x0204_0000;
 
 #[global_allocator]
 static GLOBAL_ALLOC: BlockAllocator = unsafe { BlockAllocator::new() };
 
+#[cfg(test)]
+pub unsafe fn number_of_blocks() -> u32 {
+    GLOBAL_ALLOC.number_of_blocks()
+}
+
 #[alloc_error_handler]
 fn alloc_error(layout: Layout) -> ! {
     panic!(
diff --git a/agb/src/display/example_logo.rs b/agb/src/display/example_logo.rs
index 14df97d4..3e72ad5e 100644
--- a/agb/src/display/example_logo.rs
+++ b/agb/src/display/example_logo.rs
@@ -29,6 +29,6 @@ mod tests {
 
         display_logo(&mut gfx);
 
-        crate::assert_image_output("gfx/test_logo.png");
+        crate::test_runner::assert_image_output("gfx/test_logo.png");
     }
 }
diff --git a/agb/src/interrupt.rs b/agb/src/interrupt.rs
index ec364e76..0c81656e 100644
--- a/agb/src/interrupt.rs
+++ b/agb/src/interrupt.rs
@@ -1,10 +1,11 @@
 use core::{
-    cell::{Cell, UnsafeCell},
+    cell::Cell,
     marker::{PhantomData, PhantomPinned},
-    ops::{Deref, DerefMut},
     pin::Pin,
 };
 
+use bare_metal::CriticalSection;
+
 use crate::{display::DISPLAY_STATUS, memory_mapped::MemoryMapped};
 
 #[derive(Clone, Copy)]
@@ -70,21 +71,22 @@ impl Interrupt {
 const ENABLED_INTERRUPTS: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x04000200) };
 const INTERRUPTS_ENABLED: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x04000208) };
 
-struct Disable {}
+struct Disable {
+    pre: u16,
+}
 
 impl Drop for Disable {
     fn drop(&mut self) {
-        enable_interrupts();
+        INTERRUPTS_ENABLED.set(self.pre);
     }
 }
 
 fn temporary_interrupt_disable() -> Disable {
+    let d = Disable {
+        pre: INTERRUPTS_ENABLED.get(),
+    };
     disable_interrupts();
-    Disable {}
-}
-
-fn enable_interrupts() {
-    INTERRUPTS_ENABLED.set(1);
+    d
 }
 
 fn disable_interrupts() {
@@ -158,7 +160,7 @@ pub struct InterruptClosureBounded<'a> {
 }
 
 struct InterruptClosure {
-    closure: *const (dyn Fn(Key)),
+    closure: *const (dyn Fn(&CriticalSection)),
     next: Cell<*const InterruptClosure>,
     root: *const InterruptRoot,
 }
@@ -169,7 +171,7 @@ impl InterruptRoot {
         while !c.is_null() {
             let closure_ptr = unsafe { &*c }.closure;
             let closure_ref = unsafe { &*closure_ptr };
-            closure_ref(Key());
+            closure_ref(unsafe { &CriticalSection::new() });
             c = unsafe { &*c }.next.get();
         }
     }
@@ -201,7 +203,7 @@ fn interrupt_to_root(interrupt: Interrupt) -> &'static InterruptRoot {
 }
 
 fn get_interrupt_handle_root<'a>(
-    f: &'a dyn Fn(Key),
+    f: &'a dyn Fn(&CriticalSection),
     root: &InterruptRoot,
 ) -> InterruptClosureBounded<'a> {
     InterruptClosureBounded {
@@ -218,7 +220,7 @@ fn get_interrupt_handle_root<'a>(
 /// The [add_interrupt_handler!] macro should be used instead of this function.
 /// Creates an interrupt handler from a closure.
 pub fn get_interrupt_handle(
-    f: &(dyn Fn(Key) + Send + Sync),
+    f: &(dyn Fn(&CriticalSection) + Send + Sync),
     interrupt: Interrupt,
 ) -> InterruptClosureBounded {
     let root = interrupt_to_root(interrupt);
@@ -230,22 +232,24 @@ pub fn get_interrupt_handle(
 /// Adds an interrupt handler to the interrupt table such that when that
 /// interrupt is triggered the closure is called.
 pub fn add_interrupt<'a>(interrupt: Pin<&'a InterruptClosureBounded<'a>>) {
-    let root = unsafe { &*interrupt.c.root };
-    root.add();
-    let mut c = root.next.get();
-    if c.is_null() {
-        root.next.set((&interrupt.c) as *const _);
-        return;
-    }
-    loop {
-        let p = unsafe { &*c }.next.get();
-        if p.is_null() {
-            unsafe { &*c }.next.set((&interrupt.c) as *const _);
+    free(|_| {
+        let root = unsafe { &*interrupt.c.root };
+        root.add();
+        let mut c = root.next.get();
+        if c.is_null() {
+            root.next.set((&interrupt.c) as *const _);
             return;
         }
+        loop {
+            let p = unsafe { &*c }.next.get();
+            if p.is_null() {
+                unsafe { &*c }.next.set((&interrupt.c) as *const _);
+                return;
+            }
 
-        c = p;
-    }
+            c = p;
+        }
+    })
 }
 
 #[macro_export]
@@ -270,90 +274,18 @@ macro_rules! add_interrupt_handler {
     };
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
-enum MutexState {
-    Unlocked,
-    Locked(bool),
-}
+pub fn free<F, R>(f: F) -> R
+where
+    F: FnOnce(&CriticalSection) -> R,
+{
+    let enabled = INTERRUPTS_ENABLED.get();
 
-pub struct Mutex<T> {
-    internal: UnsafeCell<T>,
-    state: UnsafeCell<MutexState>,
-}
+    disable_interrupts();
 
-#[non_exhaustive]
-pub struct Key();
+    let r = f(unsafe { &CriticalSection::new() });
 
-unsafe impl<T: Send> Send for Mutex<T> {}
-unsafe impl<T> Sync for Mutex<T> {}
-
-impl<T> Mutex<T> {
-    pub fn lock(&self) -> MutexRef<T> {
-        let state = INTERRUPTS_ENABLED.get();
-        INTERRUPTS_ENABLED.set(0);
-        assert_eq!(
-            unsafe { *self.state.get() },
-            MutexState::Unlocked,
-            "mutex must be unlocked to be able to lock it"
-        );
-        unsafe { *self.state.get() = MutexState::Locked(state != 0) };
-        MutexRef {
-            internal: &self.internal,
-            state: &self.state,
-        }
-    }
-
-    pub fn lock_with_key(&self, _key: &Key) -> MutexRef<T> {
-        assert_eq!(
-            unsafe { *self.state.get() },
-            MutexState::Unlocked,
-            "mutex must be unlocked to be able to lock it"
-        );
-        unsafe { *self.state.get() = MutexState::Locked(false) };
-        MutexRef {
-            internal: &self.internal,
-            state: &self.state,
-        }
-    }
-
-    pub const fn new(val: T) -> Self {
-        Mutex {
-            internal: UnsafeCell::new(val),
-            state: UnsafeCell::new(MutexState::Unlocked),
-        }
-    }
-}
-
-pub struct MutexRef<'a, T> {
-    internal: &'a UnsafeCell<T>,
-    state: &'a UnsafeCell<MutexState>,
-}
-
-impl<'a, T> Drop for MutexRef<'a, T> {
-    fn drop(&mut self) {
-        let state = unsafe { &mut *self.state.get() };
-
-        let prev_state = *state;
-        *state = MutexState::Unlocked;
-
-        match prev_state {
-            MutexState::Locked(b) => INTERRUPTS_ENABLED.set(b as u16),
-            MutexState::Unlocked => {}
-        }
-    }
-}
-
-impl<'a, T> Deref for MutexRef<'a, T> {
-    type Target = T;
-    fn deref(&self) -> &Self::Target {
-        unsafe { &*self.internal.get() }
-    }
-}
-
-impl<'a, T> DerefMut for MutexRef<'a, T> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        unsafe { &mut *self.internal.get() }
-    }
+    INTERRUPTS_ENABLED.set(enabled);
+    r
 }
 
 #[non_exhaustive]
@@ -382,18 +314,28 @@ impl Drop for VBlank {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use bare_metal::Mutex;
+    use core::cell::RefCell;
 
     #[test_case]
     fn test_vblank_interrupt_handler(_gba: &mut crate::Gba) {
         {
-            let counter = Mutex::new(0);
-            let counter_2 = Mutex::new(0);
-            add_interrupt_handler!(Interrupt::VBlank, |key| *counter.lock_with_key(&key) += 1);
-            add_interrupt_handler!(Interrupt::VBlank, |_| *counter_2.lock() += 1);
+            let counter = Mutex::new(RefCell::new(0));
+            let counter_2 = Mutex::new(RefCell::new(0));
+            add_interrupt_handler!(Interrupt::VBlank, |key: &CriticalSection| *counter
+                .borrow(*key)
+                .borrow_mut() +=
+                1);
+            add_interrupt_handler!(Interrupt::VBlank, |key: &CriticalSection| *counter_2
+                .borrow(*key)
+                .borrow_mut() +=
+                1);
 
             let vblank = VBlank::get();
 
-            while *counter.lock() < 100 || *counter_2.lock() < 100 {
+            while free(|key| {
+                *counter.borrow(*key).borrow() < 100 || *counter_2.borrow(*key).borrow() < 100
+            }) {
                 vblank.wait_for_vblank();
             }
         }
diff --git a/agb/src/lib.rs b/agb/src/lib.rs
index c26664c1..db1e0c50 100644
--- a/agb/src/lib.rs
+++ b/agb/src/lib.rs
@@ -2,7 +2,7 @@
 // This appears to be needed for testing to work
 #![cfg_attr(test, no_main)]
 #![cfg_attr(test, feature(custom_test_frameworks))]
-#![cfg_attr(test, test_runner(crate::test_runner))]
+#![cfg_attr(test, test_runner(crate::test_runner::test_runner))]
 #![cfg_attr(test, reexport_test_harness_main = "test_main")]
 #![deny(clippy::all)]
 #![feature(alloc_error_handler)]
@@ -224,89 +224,96 @@ impl Gba {
     }
 }
 
-#[doc(hidden)]
-pub trait Testable {
-    fn run(&self, gba: &mut Gba);
-}
+#[cfg(test)]
+mod test_runner {
+    use super::*;
 
-impl<T> Testable for T
-where
-    T: Fn(&mut Gba),
-{
-    fn run(&self, gba: &mut Gba) {
+    #[doc(hidden)]
+    pub trait Testable {
+        fn run(&self, gba: &mut Gba);
+    }
+
+    impl<T> Testable for T
+    where
+        T: Fn(&mut Gba),
+    {
+        fn run(&self, gba: &mut Gba) {
+            let mut mgba = mgba::Mgba::new().unwrap();
+            mgba.print(
+                format_args!("{}...", core::any::type_name::<T>()),
+                mgba::DebugLevel::Info,
+            )
+            .unwrap();
+            mgba::number_of_cycles_tagged(785);
+            self(gba);
+            mgba::number_of_cycles_tagged(785);
+
+            assert!(
+                unsafe { agb_alloc::number_of_blocks() } < 2,
+                "memory is being leaked, there are {} blocks",
+                unsafe { agb_alloc::number_of_blocks() }
+            );
+
+            mgba.print(format_args!("[ok]"), mgba::DebugLevel::Info)
+                .unwrap();
+        }
+    }
+
+    #[panic_handler]
+    fn panic_implementation(info: &core::panic::PanicInfo) -> ! {
+        if let Some(mut mgba) = mgba::Mgba::new() {
+            mgba.print(format_args!("[failed]"), mgba::DebugLevel::Error)
+                .unwrap();
+            mgba.print(format_args!("Error: {}", info), mgba::DebugLevel::Fatal)
+                .unwrap();
+        }
+
+        loop {}
+    }
+
+    static mut TEST_GBA: Option<Gba> = None;
+
+    #[doc(hidden)]
+    pub fn test_runner(tests: &[&dyn Testable]) {
         let mut mgba = mgba::Mgba::new().unwrap();
         mgba.print(
-            format_args!("{}...", core::any::type_name::<T>()),
+            format_args!("Running {} tests", tests.len()),
             mgba::DebugLevel::Info,
         )
         .unwrap();
-        mgba::number_of_cycles_tagged(785);
-        self(gba);
-        mgba::number_of_cycles_tagged(785);
-        mgba.print(format_args!("[ok]"), mgba::DebugLevel::Info)
-            .unwrap();
-    }
-}
 
-#[panic_handler]
-#[cfg(test)]
-fn panic_implementation(info: &core::panic::PanicInfo) -> ! {
-    if let Some(mut mgba) = mgba::Mgba::new() {
-        mgba.print(format_args!("[failed]"), mgba::DebugLevel::Error)
-            .unwrap();
-        mgba.print(format_args!("Error: {}", info), mgba::DebugLevel::Fatal)
-            .unwrap();
+        let gba = unsafe { TEST_GBA.as_mut() }.unwrap();
+
+        for test in tests {
+            test.run(gba);
+        }
+
+        mgba.print(
+            format_args!("Tests finished successfully"),
+            mgba::DebugLevel::Info,
+        )
+        .unwrap();
     }
 
-    loop {}
-}
-
-#[cfg(test)]
-static mut TEST_GBA: Option<Gba> = None;
-
-#[doc(hidden)]
-#[cfg(test)]
-pub fn test_runner(tests: &[&dyn Testable]) {
-    let mut mgba = mgba::Mgba::new().unwrap();
-    mgba.print(
-        format_args!("Running {} tests", tests.len()),
-        mgba::DebugLevel::Info,
-    )
-    .unwrap();
-
-    let mut gba = unsafe { TEST_GBA.as_mut() }.unwrap();
-
-    for test in tests {
-        test.run(&mut gba);
+    #[entry]
+    fn agb_test_main(gba: Gba) -> ! {
+        unsafe { TEST_GBA = Some(gba) };
+        test_main();
+        #[allow(clippy::empty_loop)]
+        loop {}
     }
 
-    mgba.print(
-        format_args!("Tests finished successfully"),
-        mgba::DebugLevel::Info,
-    )
-    .unwrap();
-}
-
-#[cfg(test)]
-#[entry]
-fn agb_test_main(gba: Gba) -> ! {
-    unsafe { TEST_GBA = Some(gba) };
-    test_main();
-    #[allow(clippy::empty_loop)]
-    loop {}
-}
-
-#[cfg(test)]
-fn assert_image_output(image: &str) {
-    display::busy_wait_for_vblank();
-    display::busy_wait_for_vblank();
-    let mut mgba = crate::mgba::Mgba::new().unwrap();
-    mgba.print(
-        format_args!("image:{}", image),
-        crate::mgba::DebugLevel::Info,
-    )
-    .unwrap();
-    display::busy_wait_for_vblank();
+    pub fn assert_image_output(image: &str) {
+        display::busy_wait_for_vblank();
+        display::busy_wait_for_vblank();
+        let mut mgba = crate::mgba::Mgba::new().unwrap();
+        mgba.print(
+            format_args!("image:{}", image),
+            crate::mgba::DebugLevel::Info,
+        )
+        .unwrap();
+        display::busy_wait_for_vblank();
+    }
 }
 
 #[cfg(test)]