diff --git a/src/isa-thumb.c b/src/isa-thumb.c
index 946b37bd1..e5092f552 100644
--- a/src/isa-thumb.c
+++ b/src/isa-thumb.c
@@ -223,7 +223,7 @@ DEFINE_DATA_FORM_5_INSTRUCTION_THUMB(MVN, ARM_STUB)
 	DEFINE_INSTRUCTION_WITH_HIGH_EX_THUMB(NAME ## 10, 8, 0, BODY) \
 	DEFINE_INSTRUCTION_WITH_HIGH_EX_THUMB(NAME ## 11, 8, 8, BODY)
 
-DEFINE_INSTRUCTION_WITH_HIGH_THUMB(ADD4, ARM_STUB)
+DEFINE_INSTRUCTION_WITH_HIGH_THUMB(ADD4, cpu->gprs[rd] += cpu->gprs[rm])
 DEFINE_INSTRUCTION_WITH_HIGH_THUMB(CMP3, int32_t aluOut = cpu->gprs[rd] - cpu->gprs[rm]; THUMB_SUBTRACTION_S(cpu->gprs[rd], cpu->gprs[rm], aluOut))
 DEFINE_INSTRUCTION_WITH_HIGH_THUMB(MOV3, cpu->gprs[rd] = cpu->gprs[rm])