diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index ac31a91..d81d247 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -150,13 +150,13 @@ agb_arm_func agb_rs__init_buffer
     push {r4-r5}
 
     @ zero registers r3-r5
-    mov r2, #constant_zero
+    ldr r2, =constant_zero
     ldm r2, {r3-r5,r12}
 
 1:
     @ zero 4 words worth of the buffer
-    stmia r0, {r3-r5,r12}
-    subs r1, r1, #16
+    stmia r0!, {r3-r5,r12}
+    subs r1, r1, #(4 * 4)
     @ loop if we haven't zeroed everything
     bne 1b
 
diff --git a/agb/src/sound/mixer/sw_mixer.rs b/agb/src/sound/mixer/sw_mixer.rs
index 02b54fe..c8ed7b4 100644
--- a/agb/src/sound/mixer/sw_mixer.rs
+++ b/agb/src/sound/mixer/sw_mixer.rs
@@ -1,4 +1,6 @@
 use core::cell::RefCell;
+use core::mem;
+use core::mem::MaybeUninit;
 
 use bare_metal::{CriticalSection, Mutex};
 
@@ -27,6 +29,8 @@ extern "C" {
     fn agb_rs__mixer_add_stereo(sound_data: *const u8, sound_buffer: *mut Num<i16, 4>);
 
     fn agb_rs__mixer_collapse(sound_buffer: *mut i8, input_buffer: *const Num<i16, 4>);
+
+    fn agb_rs__init_buffer(buffer: *mut MaybeUninit<Num<i16, 4>>, size_in_bytes: usize);
 }
 
 pub struct Mixer {
@@ -231,8 +235,28 @@ impl MixerBuffer {
     }
 
     fn write_channels<'a>(&mut self, channels: impl Iterator<Item = &'a mut SoundChannel>) {
-        let mut buffer: [Num<i16, 4>; constants::SOUND_BUFFER_SIZE * 2] =
-            [Num::new(0); constants::SOUND_BUFFER_SIZE * 2];
+        // This code is equivalent to:
+        // let mut buffer: [Num<i16, 4>; constants::SOUND_BUFFER_SIZE * 2] =
+        //     [Num::new(0); constants::SOUND_BUFFER_SIZE * 2];
+        // but the above uses approximately 7% of the CPU time if running at 32kHz
+        let mut buffer: [Num<i16, 4>; constants::SOUND_BUFFER_SIZE * 2] = {
+            // Create an uninitialized array of `MaybeUninit`. The `assume_init` is
+            // safe because the type we are claiming to have initialized here is a
+            // bunch of `MaybeUninit`s, which do not require initialization.
+            let mut data: [MaybeUninit<Num<i16, 4>>; constants::SOUND_BUFFER_SIZE * 2] =
+                unsafe { MaybeUninit::uninit().assume_init() };
+
+            // Actually init the array (by filling it with zeros) and then transmute it (which is safe because
+            // we have now zeroed everything)
+            unsafe {
+                agb_rs__init_buffer(
+                    data.as_mut_ptr(),
+                    mem::size_of::<Num<i16, 4>>() * data.len(),
+                );
+
+                mem::transmute(data)
+            }
+        };
 
         for channel in channels {
             if channel.is_done {