diff --git a/CHANGES b/CHANGES
index c603347be..fa56a39e3 100644
--- a/CHANGES
+++ b/CHANGES
@@ -71,6 +71,7 @@ Misc:
  - Qt, OpenGL: Disable integer scaling for dimensions that don't fit
  - Feature: Switch from ImageMagick to FFmpeg for GIF generation
  - OpenGL: Only resize textures when needed
+ - GBA BIOS: Fix clobbered registers in CpuSet (fixes mgba.io/i/1531)
 
 0.7.3: (2019-09-15)
 Emulation fixes:
diff --git a/src/gba/hle-bios.c b/src/gba/hle-bios.c
index a6a5382e9..776c3d550 100644
--- a/src/gba/hle-bios.c
+++ b/src/gba/hle-bios.c
@@ -6,7 +6,7 @@ const uint8_t hleBios[SIZE_BIOS] = {
 	0x06, 0x00, 0x00, 0xea, 0xfe, 0xff, 0xff, 0xea, 0x0b, 0x00, 0x00, 0xea,
 	0xfe, 0xff, 0xff, 0xea, 0xfe, 0xff, 0xff, 0xea, 0x00, 0x00, 0xa0, 0xe1,
 	0x2c, 0x00, 0x00, 0xea, 0xfe, 0xff, 0xff, 0xea, 0x02, 0x03, 0xa0, 0xe3,
-	0x03, 0x10, 0xd0, 0xe5, 0xea, 0x00, 0x51, 0xe3, 0xec, 0x01, 0x9f, 0x15,
+	0x03, 0x10, 0xd0, 0xe5, 0xea, 0x00, 0x51, 0xe3, 0xf8, 0x01, 0x9f, 0x15,
 	0x10, 0xff, 0x2f, 0xe1, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf0, 0x29, 0xe1,
 	0x00, 0x00, 0x5d, 0xe3, 0x01, 0xd3, 0xa0, 0x03, 0x20, 0xd0, 0x4d, 0x02,
 	0x00, 0x58, 0x2d, 0xe9, 0x02, 0xb0, 0x5e, 0xe5, 0x9c, 0xc0, 0xa0, 0xe3,
@@ -20,7 +20,7 @@ const uint8_t hleBios[SIZE_BIOS] = {
 	0x00, 0x00, 0x00, 0x00, 0xf8, 0x00, 0x00, 0x00, 0xf0, 0x00, 0x00, 0x00,
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x01, 0x00, 0x00,
-	0xc8, 0x01, 0x00, 0x00, 0x0f, 0x50, 0x2d, 0xe9, 0x01, 0x03, 0xa0, 0xe3,
+	0xd4, 0x01, 0x00, 0x00, 0x0f, 0x50, 0x2d, 0xe9, 0x01, 0x03, 0xa0, 0xe3,
 	0x00, 0xe0, 0x8f, 0xe2, 0x04, 0xf0, 0x10, 0xe5, 0x0f, 0x50, 0xbd, 0xe8,
 	0x04, 0xf0, 0x5e, 0xe2, 0x00, 0x00, 0x00, 0x00, 0x02, 0xc0, 0x5e, 0xe5,
 	0x01, 0x00, 0xa0, 0xe3, 0x01, 0x10, 0xa0, 0xe3, 0x0c, 0x40, 0x2d, 0xe9,
@@ -29,18 +29,19 @@ const uint8_t hleBios[SIZE_BIOS] = {
 	0x01, 0x30, 0xc3, 0xe1, 0xb8, 0x30, 0x4c, 0xe1, 0x01, 0x03, 0xcc, 0xe5,
 	0x08, 0x02, 0xcc, 0xe5, 0xb8, 0x30, 0x5c, 0xe1, 0x01, 0x30, 0x13, 0xe0,
 	0x01, 0x30, 0x23, 0x10, 0xb8, 0x30, 0x4c, 0x11, 0x08, 0x22, 0xcc, 0xe5,
-	0xf7, 0xff, 0xff, 0x0a, 0x0c, 0x80, 0xbd, 0xe8, 0x00, 0x40, 0x2d, 0xe9,
-	0x02, 0x36, 0xa0, 0xe1, 0x01, 0x04, 0x12, 0xe3, 0x0f, 0x00, 0x00, 0x0a,
-	0x01, 0x03, 0x12, 0xe3, 0x05, 0x00, 0x00, 0x0a, 0x23, 0x35, 0x81, 0xe0,
-	0x04, 0x00, 0xb0, 0xe8, 0x03, 0x00, 0x51, 0xe1, 0x04, 0x00, 0xa1, 0xb8,
-	0xfc, 0xff, 0xff, 0xba, 0x14, 0x00, 0x00, 0xea, 0x01, 0x00, 0xc0, 0xe3,
-	0x01, 0x10, 0xc1, 0xe3, 0xa3, 0x35, 0x81, 0xe0, 0xb0, 0x20, 0xd0, 0xe1,
-	0x03, 0x00, 0x51, 0xe1, 0xb2, 0x20, 0xc1, 0xb0, 0xfc, 0xff, 0xff, 0xba,
-	0x0c, 0x00, 0x00, 0xea, 0x01, 0x03, 0x12, 0xe3, 0x05, 0x00, 0x00, 0x0a,
-	0x23, 0x35, 0x81, 0xe0, 0x03, 0x00, 0x51, 0xe1, 0x04, 0x00, 0xb0, 0xb8,
-	0x04, 0x00, 0xa1, 0xb8, 0xfb, 0xff, 0xff, 0xba, 0x04, 0x00, 0x00, 0xea,
-	0xa3, 0x35, 0x81, 0xe0, 0x03, 0x00, 0x51, 0xe1, 0xb2, 0x20, 0xd0, 0xb0,
-	0xb2, 0x20, 0xc1, 0xb0, 0xfb, 0xff, 0xff, 0xba, 0x00, 0x80, 0xbd, 0xe8,
+	0xf7, 0xff, 0xff, 0x0a, 0x0c, 0x80, 0xbd, 0xe8, 0x30, 0x40, 0x2d, 0xe9,
+	0x02, 0x46, 0xa0, 0xe1, 0x00, 0xc0, 0xa0, 0xe1, 0x01, 0x50, 0xa0, 0xe1,
+	0x01, 0x04, 0x12, 0xe3, 0x0f, 0x00, 0x00, 0x0a, 0x01, 0x03, 0x12, 0xe3,
+	0x05, 0x00, 0x00, 0x0a, 0x24, 0x45, 0x85, 0xe0, 0x08, 0x00, 0xbc, 0xe8,
+	0x04, 0x00, 0x55, 0xe1, 0x08, 0x00, 0xa5, 0xb8, 0xfc, 0xff, 0xff, 0xba,
+	0x14, 0x00, 0x00, 0xea, 0x01, 0xc0, 0xcc, 0xe3, 0x01, 0x50, 0xc5, 0xe3,
+	0xa4, 0x45, 0x85, 0xe0, 0xb0, 0x30, 0xdc, 0xe1, 0x04, 0x00, 0x55, 0xe1,
+	0xb2, 0x30, 0xc5, 0xb0, 0xfc, 0xff, 0xff, 0xba, 0x0c, 0x00, 0x00, 0xea,
+	0x01, 0x03, 0x12, 0xe3, 0x05, 0x00, 0x00, 0x0a, 0x24, 0x45, 0x85, 0xe0,
+	0x04, 0x00, 0x55, 0xe1, 0x08, 0x00, 0xbc, 0xb8, 0x08, 0x00, 0xa5, 0xb8,
+	0xfb, 0xff, 0xff, 0xba, 0x04, 0x00, 0x00, 0xea, 0xa4, 0x45, 0x85, 0xe0,
+	0x04, 0x00, 0x55, 0xe1, 0xb2, 0x30, 0xdc, 0xb0, 0xb2, 0x30, 0xc5, 0xb0,
+	0xfb, 0xff, 0xff, 0xba, 0x17, 0x3e, 0xa0, 0xe3, 0x30, 0x80, 0xbd, 0xe8,
 	0xf0, 0x47, 0x2d, 0xe9, 0x01, 0x04, 0x12, 0xe3, 0x02, 0x36, 0xa0, 0xe1,
 	0x23, 0x25, 0x81, 0xe0, 0x0b, 0x00, 0x00, 0x0a, 0x00, 0x30, 0x90, 0xe5,
 	0x03, 0x40, 0xa0, 0xe1, 0x03, 0x50, 0xa0, 0xe1, 0x03, 0x60, 0xa0, 0xe1,
diff --git a/src/gba/hle-bios.s b/src/gba/hle-bios.s
index e10947c96..f14ddee90 100644
--- a/src/gba/hle-bios.s
+++ b/src/gba/hle-bios.s
@@ -106,54 +106,57 @@ beq    0b
 ldmfd  sp!, {r2-r3, pc}
 
 CpuSet:
-stmfd  sp!, {lr}
-mov    r3, r2, lsl #12
+stmfd  sp!, {r4, r5, lr}
+mov    r4, r2, lsl #12
+mov    r12, r0
+mov    r5, r1
 tst    r2, #0x01000000
 beq    0f
-# Fill
+@ Fill
 tst    r2, #0x04000000
 beq    1f
-# Word
-add    r3, r1, r3, lsr #10
-ldmia  r0!, {r2}
+@ Word
+add    r4, r5, r4, lsr #10
+ldmia  r12!, {r3}
 2:
-cmp    r1, r3
-stmltia  r1!, {r2}
+cmp    r5, r4
+stmltia  r5!, {r3}
 blt    2b
 b      3f
-# Halfword
+@ Halfword
 1:
-bic    r0, #1
-bic    r1, #1
-add    r3, r1, r3, lsr #11
-ldrh   r2, [r0]
+bic    r12, #1
+bic    r5, #1
+add    r4, r5, r4, lsr #11
+ldrh   r3, [r12]
 2:
-cmp    r1, r3
-strlth r2, [r1], #2
+cmp    r5, r4
+strlth r3, [r5], #2
 blt    2b
 b      3f
-# Copy
+@ Copy
 0:
 tst    r2, #0x04000000
 beq    1f
-# Word
-add    r3, r1, r3, lsr #10
+@ Word
+add    r4, r5, r4, lsr #10
 2:
-cmp    r1, r3
-ldmltia r0!, {r2}
-stmltia r1!, {r2}
+cmp    r5, r4
+ldmltia r12!, {r3}
+stmltia r5!, {r3}
 blt    2b
 b      3f
-# Halfword
+@ Halfword
 1:
-add    r3, r1, r3, lsr #11
+add    r4, r5, r4, lsr #11
 2:
-cmp    r1, r3
-ldrlth r2, [r0], #2
-strlth r2, [r1], #2
+cmp    r5, r4
+ldrlth r3, [r12], #2
+strlth r3, [r5], #2
 blt    2b
 3:
-ldmfd  sp!, {pc}
+mov    r3, #0x170  @ Match official BIOS's clobbered r3
+ldmfd  sp!, {r4, r5, pc}
 
 CpuFastSet:
 stmfd  sp!, {r4-r10, lr}