diff --git a/agb-fixnum/src/lib.rs b/agb-fixnum/src/lib.rs
index f9df1f38..a4196b24 100644
--- a/agb-fixnum/src/lib.rs
+++ b/agb-fixnum/src/lib.rs
@@ -79,6 +79,8 @@ pub trait FixedWidthUnsignedInteger:
     fn ten() -> Self;
     /// Converts an i32 to it's own representation, panics on failure
     fn from_as_i32(v: i32) -> Self;
+    /// Returns (a * b) >> N
+    fn upcast_multiply(a: Self, b: Self, n: usize) -> Self;
 }
 
 /// Trait for an integer that includes negation
@@ -89,7 +91,7 @@ pub trait FixedWidthSignedInteger: FixedWidthUnsignedInteger + Neg<Output = Self
 }
 
 macro_rules! fixed_width_unsigned_integer_impl {
-    ($T: ty) => {
+    ($T: ty, $Upcast: ty) => {
         impl FixedWidthUnsignedInteger for $T {
             #[inline(always)]
             fn zero() -> Self {
@@ -107,6 +109,10 @@ macro_rules! fixed_width_unsigned_integer_impl {
             fn from_as_i32(v: i32) -> Self {
                 v as $T
             }
+            #[inline(always)]
+            fn upcast_multiply(a: Self, b: Self, n: usize) -> Self {
+                (((a as $Upcast) * (b as $Upcast)) >> n) as $T
+            }
         }
     };
 }
@@ -122,12 +128,11 @@ macro_rules! fixed_width_signed_integer_impl {
     };
 }
 
-fixed_width_unsigned_integer_impl!(u8);
-fixed_width_unsigned_integer_impl!(i16);
-fixed_width_unsigned_integer_impl!(u16);
-fixed_width_unsigned_integer_impl!(i32);
-fixed_width_unsigned_integer_impl!(u32);
-fixed_width_unsigned_integer_impl!(usize);
+fixed_width_unsigned_integer_impl!(u8, u32);
+fixed_width_unsigned_integer_impl!(i16, i32);
+fixed_width_unsigned_integer_impl!(u16, u32);
+fixed_width_unsigned_integer_impl!(i32, i64);
+fixed_width_unsigned_integer_impl!(u32, u64);
 
 fixed_width_signed_integer_impl!(i16);
 fixed_width_signed_integer_impl!(i32);
@@ -204,9 +209,7 @@ where
 {
     type Output = Self;
     fn mul(self, rhs: Num<I, N>) -> Self::Output {
-        Num(((self.floor() * rhs.floor()) << N)
-            + (self.floor() * rhs.frac() + rhs.floor() * self.frac())
-            + ((self.frac() * rhs.frac()) >> N))
+        Num(I::upcast_multiply(self.0, rhs.0, N))
     }
 }
 
diff --git a/agb/examples/mixer_basic.rs b/agb/examples/mixer_basic.rs
index 80375d77..97403e8b 100644
--- a/agb/examples/mixer_basic.rs
+++ b/agb/examples/mixer_basic.rs
@@ -26,7 +26,7 @@ fn main(mut gba: Gba) -> ! {
         {
             if let Some(channel) = mixer.channel(&channel_id) {
                 let half: Num<i16, 4> = num!(0.5);
-                let half_usize: Num<usize, 8> = num!(0.5);
+                let half_usize: Num<u32, 8> = num!(0.5);
                 match input.x_tri() {
                     Tri::Negative => channel.panning(-half),
                     Tri::Zero => channel.panning(0),
diff --git a/agb/src/sound/mixer/mod.rs b/agb/src/sound/mixer/mod.rs
index ca2a36ab..0bff6c50 100644
--- a/agb/src/sound/mixer/mod.rs
+++ b/agb/src/sound/mixer/mod.rs
@@ -224,10 +224,10 @@ impl Frequency {
 /// ```
 pub struct SoundChannel {
     data: &'static [u8],
-    pos: Num<usize, 8>,
+    pos: Num<u32, 8>,
     should_loop: bool,
 
-    playback_speed: Num<usize, 8>,
+    playback_speed: Num<u32, 8>,
     volume: Num<i16, 4>, // between 0 and 1
 
     panning: Num<i16, 4>, // between -1 and 1
@@ -336,7 +336,7 @@ impl SoundChannel {
     /// Note that this only works for mono sounds. Stereo sounds will not change
     /// how fast they play.
     #[inline(always)]
-    pub fn playback(&mut self, playback_speed: impl Into<Num<usize, 8>>) -> &mut Self {
+    pub fn playback(&mut self, playback_speed: impl Into<Num<u32, 8>>) -> &mut Self {
         self.playback_speed = playback_speed.into();
         self
     }
@@ -392,13 +392,13 @@ impl SoundChannel {
     /// Gets how far along the sound has played.
     #[inline]
     #[must_use]
-    pub fn pos(&self) -> Num<usize, 8> {
+    pub fn pos(&self) -> Num<u32, 8> {
         self.pos
     }
 
     /// Sets the playback position
     #[inline]
-    pub fn set_pos(&mut self, pos: impl Into<Num<usize, 8>>) -> &mut Self {
+    pub fn set_pos(&mut self, pos: impl Into<Num<u32, 8>>) -> &mut Self {
         self.pos = pos.into();
         self
     }
diff --git a/agb/src/sound/mixer/sw_mixer.rs b/agb/src/sound/mixer/sw_mixer.rs
index 8984f842..1962fef9 100644
--- a/agb/src/sound/mixer/sw_mixer.rs
+++ b/agb/src/sound/mixer/sw_mixer.rs
@@ -24,7 +24,7 @@ extern "C" {
     fn agb_rs__mixer_add(
         sound_data: *const u8,
         sound_buffer: *mut Num<i16, 4>,
-        playback_speed: Num<usize, 8>,
+        playback_speed: Num<u32, 8>,
         left_amount: Num<i16, 4>,
         right_amount: Num<i16, 4>,
     );
@@ -415,8 +415,8 @@ impl MixerBuffer {
                 channel.playback_speed
             };
 
-            if (channel.pos + playback_speed * self.frequency.buffer_size()).floor()
-                >= channel.data.len()
+            if (channel.pos + playback_speed * self.frequency.buffer_size() as u32).floor()
+                >= channel.data.len() as u32
             {
                 // TODO: This should probably play what's left rather than skip the last bit
                 if channel.should_loop {
@@ -431,7 +431,7 @@ impl MixerBuffer {
                 if channel.is_stereo {
                     unsafe {
                         agb_rs__mixer_add_stereo(
-                            channel.data.as_ptr().add(channel.pos.floor()),
+                            channel.data.as_ptr().add(channel.pos.floor() as usize),
                             working_buffer.as_mut_ptr(),
                             channel.volume,
                         );
@@ -442,7 +442,7 @@ impl MixerBuffer {
 
                     unsafe {
                         agb_rs__mixer_add(
-                            channel.data.as_ptr().add(channel.pos.floor()),
+                            channel.data.as_ptr().add(channel.pos.floor() as usize),
                             working_buffer.as_mut_ptr(),
                             playback_speed,
                             left_amount,
@@ -452,7 +452,7 @@ impl MixerBuffer {
                 }
             }
 
-            channel.pos += playback_speed * self.frequency.buffer_size();
+            channel.pos += playback_speed * self.frequency.buffer_size() as u32;
         }
 
         let write_buffer = free(|cs| self.state.borrow(cs).borrow_mut().active_advanced());