diff --git a/arch/X86/X86Disassembler.c b/arch/X86/X86Disassembler.c
index c4282346..e04837fa 100644
--- a/arch/X86/X86Disassembler.c
+++ b/arch/X86/X86Disassembler.c
@@ -802,9 +802,7 @@ bool X86_getInstruction(csh ud, const uint8_t *code, size_t code_len,
 				}
 			}
 
-			if (insn.prefixPresent[0xf0] || insn.prefixPresent[0xf2] ||
-					insn.prefixPresent[0xf3])
-				instr->x86_lock_rep = true;
+			instr->x86_lock_rep = insn.x86_lock_rep;
 
 			// save immediate size to print immediate properly
 			instr->x86_imm_size = insn.immediateSize;
diff --git a/arch/X86/X86DisassemblerDecoder.c b/arch/X86/X86DisassemblerDecoder.c
index 68fbd414..72d347ef 100644
--- a/arch/X86/X86DisassemblerDecoder.c
+++ b/arch/X86/X86DisassemblerDecoder.c
@@ -531,6 +531,8 @@ static int readPrefixes(struct InternalInstruction* insn)
 			dbgprintf(insn, "Found prefix 0x%hhx", byte);
 	}
 
+	insn->x86_lock_rep = prefixGroups[0];
+
 	insn->vectorExtensionType = TYPE_NO_VEX_XOP;
 
 	if (byte == 0x62) {
diff --git a/arch/X86/X86DisassemblerDecoder.h b/arch/X86/X86DisassemblerDecoder.h
index 6387f896..7c44c9d5 100644
--- a/arch/X86/X86DisassemblerDecoder.h
+++ b/arch/X86/X86DisassemblerDecoder.h
@@ -635,6 +635,9 @@ typedef struct InternalInstruction {
   uint8_t                       firstByte;     // save the first byte in stream
   uint8_t                       orgModRM;  // save original modRM because we will modify modRM
 
+  // does this instruction contain LOC/REP/REPNE prefix?
+  bool x86_lock_rep;
+
   /* The SIB byte, used for more complex 32- or 64-bit memory operands */
   BOOL                          consumedSIB;
   uint8_t                       sib;
diff --git a/arch/X86/X86Mapping.c b/arch/X86/X86Mapping.c
index 7b59d10e..7ce3da2a 100644
--- a/arch/X86/X86Mapping.c
+++ b/arch/X86/X86Mapping.c
@@ -41723,8 +41723,8 @@ bool X86_lockrep(MCInst *MI, SStream *O)
 					break;
 				case 0xf2:
 #ifndef CAPSTONE_X86_REDUCE
-					if (MI->Opcode == X86_MULPDrr) {
-						MI->Opcode = X86_MULSDrr;
+					if (MCInst_getOpcode(MI) == X86_MULPDrr) {
+						MCInst_setOpcode(MI, X86_MULSDrr);
 #ifndef CAPSTONE_DIET
 						SStream_concat(O, "mulsd\t");
 #endif
@@ -41742,8 +41742,8 @@ bool X86_lockrep(MCInst *MI, SStream *O)
 					break;
 				case 0xf3:
 #ifndef CAPSTONE_X86_REDUCE
-					if (MI->Opcode == X86_MULPDrr) {
-						MI->Opcode = X86_MULSSrr;
+					if (MCInst_getOpcode(MI) == X86_MULPDrr) {
+						MCInst_setOpcode(MI, X86_MULSSrr);
 #ifndef CAPSTONE_DIET
 						SStream_concat(O, "mulss\t");
 #endif