diff --git a/lib/soft386/opcodes.c b/lib/soft386/opcodes.c
index 099ef3b3195..120662b0620 100644
--- a/lib/soft386/opcodes.c
+++ b/lib/soft386/opcodes.c
@@ -1152,12 +1152,13 @@ SOFT386_OPCODE_HANDLER(Soft386OpcodeMovRegImm)
     /* Make sure this is the right instruction */
     ASSERT((Opcode & 0xF8) == 0xB8);
 
-    if (State->PrefixFlags == SOFT386_PREFIX_OPSIZE)
+    if (State->PrefixFlags & SOFT386_PREFIX_OPSIZE)
     {
         /* The OPSIZE prefix toggles the size */
         Size = !Size;
     }
-    else if (State->PrefixFlags != 0)
+
+    if (State->PrefixFlags & SOFT386_PREFIX_LOCK)
     {
         /* Invalid prefix */
         Soft386Exception(State, SOFT386_EXCEPTION_UD);