diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index 66bec925..2299a22b 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -157,12 +157,12 @@ agb_arm_func agb_rs__mixer_collapse
     push {{r4-r11,lr}}
 
 CONST_0   .req r7
-CONST_127 .req r8
+CONST_128 .req r8
 TEMP      .req r10
 SWAP_SIGN .req r11
 
     ldr CONST_0, =0
-    ldr CONST_127, =127
+    ldr CONST_128, =128
     ldr SWAP_SIGN, =0x80808080
 
     mov r4, r2
@@ -192,8 +192,8 @@ SWAP_SIGN .req r11
 
 .macro load_sample left_reg:req right_reg:req
     mov \right_reg, \left_reg, lsl #16                 @ push the sample 16 bits first
-    add \right_reg, CONST_127, \right_reg, asr #20     @ move right sample back to being the correct value
-    add \left_reg, CONST_127, \left_reg, asr #20       @ now we only have the left sample
+    add \right_reg, CONST_128, \right_reg, asr #20     @ move right sample back to being the correct value
+    add \left_reg, CONST_128, \left_reg, asr #20       @ now we only have the left sample
 
     clamp_s8 \left_reg                                 @ clamp the audio to 8 bit values
     clamp_s8 \right_reg
diff --git a/agb/src/sound/mixer/sw_mixer.rs b/agb/src/sound/mixer/sw_mixer.rs
index 5c01181b..2b75734e 100644
--- a/agb/src/sound/mixer/sw_mixer.rs
+++ b/agb/src/sound/mixer/sw_mixer.rs
@@ -470,3 +470,64 @@ impl MixerBuffer {
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use crate::fixnum::num;
+    use alloc::vec;
+
+    use super::*;
+
+    #[test_case]
+    fn collapse_should_correctly_reduce_size_of_input(_: &mut crate::Gba) {
+        let input: &[Num<i16, 4>] = &[
+            num!(10.0),
+            num!(10.0),
+            num!(5.0),
+            num!(5.0),
+            num!(-10.0),
+            num!(-10.5),
+            num!(-5.9),
+            num!(-5.2),
+            num!(0.0),
+            num!(1.1),
+            num!(2.2),
+            num!(3.3),
+            num!(155.4),
+            num!(-230.5),
+            num!(400.6),
+            num!(-700.7),
+            num!(10.0),
+            num!(10.0),
+            num!(5.0),
+            num!(5.0),
+            num!(-10.0),
+            num!(-10.5),
+            num!(-5.9),
+            num!(-5.2),
+            num!(0.0),
+            num!(1.1),
+            num!(2.2),
+            num!(3.3),
+            num!(155.4),
+            num!(-230.5),
+            num!(400.6),
+            num!(-700.7),
+        ];
+
+        let mut output_buffer = vec![0i8; input.len()];
+
+        unsafe {
+            agb_rs__mixer_collapse(output_buffer.as_mut_ptr(), input.as_ptr(), input.len() / 2);
+        }
+
+        // output will be unzipped, so input is LRLRLRLRLRLRLR... and output is LLLLLLRRRRRR
+        assert_eq!(
+            output_buffer,
+            &[
+                10, 5, -10, -6, 0, 2, 127, 127, 10, 5, -10, -6, 0, 2, 127, 127, 10, 5, -11, -6, 1,
+                3, -128, -128, 10, 5, -11, -6, 1, 3, -128, -128
+            ]
+        );
+    }
+}