diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
index a50f57dbaa..f4192f1006 100644
--- a/target/i386/tcg/decode-new.c.inc
+++ b/target/i386/tcg/decode-new.c.inc
@@ -335,6 +335,8 @@ static void decode_group9(DisasContext *s, CPUX86State *env, X86OpEntry *entry,
         *entry = group9_reg;
     } else if (op == 1) {
         *entry = REX_W(s) ? cmpxchg16b : cmpxchg8b;
+    } else {
+        *entry = UNKNOWN_OPCODE;
     }
 }