diff --git a/include/mgba/internal/arm/isa-thumb.h b/include/mgba/internal/arm/isa-thumb.h
index 330a4faf8..69839d47a 100644
--- a/include/mgba/internal/arm/isa-thumb.h
+++ b/include/mgba/internal/arm/isa-thumb.h
@@ -12,7 +12,7 @@ CXX_GUARD_START
 
 struct ARMCore;
 
-typedef void (*ThumbInstruction)(struct ARMCore*, uint16_t opcode);
+typedef void (*ThumbInstruction)(struct ARMCore*, unsigned opcode);
 extern const ThumbInstruction _thumbTable[0x400];
 
 CXX_GUARD_END
diff --git a/src/arm/isa-thumb.c b/src/arm/isa-thumb.c
index 54faf6ddc..3f48510e7 100644
--- a/src/arm/isa-thumb.c
+++ b/src/arm/isa-thumb.c
@@ -48,7 +48,7 @@
 	currentCycles += cpu->memory.activeNonseqCycles16 - cpu->memory.activeSeqCycles16;
 
 #define DEFINE_INSTRUCTION_THUMB(NAME, BODY) \
-	static void _ThumbInstruction ## NAME (struct ARMCore* cpu, uint16_t opcode) {  \
+	static void _ThumbInstruction ## NAME (struct ARMCore* cpu, unsigned opcode) {  \
 		int currentCycles = THUMB_PREFETCH_CYCLES; \
 		BODY; \
 		cpu->cycles += currentCycles; \