diff --git a/src/gba/GBA-arm.cpp b/src/gba/GBA-arm.cpp
index 58da037b..6063ce46 100644
--- a/src/gba/GBA-arm.cpp
+++ b/src/gba/GBA-arm.cpp
@@ -964,9 +964,8 @@ static void count(u32 opcode, int cond_res)
 #endif
 #ifndef OP_RSB
  #define OP_RSB \
-    u32 lhs = reg[(opcode>>16)&15].I;                   \
-    u32 rhs = value;                                    \
-    u32 res = rhs - lhs;                                \
+    u32 lhs = value;                                    \
+    u32 rhs = reg[(opcode>>16)&15].I;                   \
     reg[dest].I = res;
 #endif
 #ifndef OP_RSBS