diff --git a/kernel/x86_emulate.c b/kernel/x86_emulate.c
index f2a696d..7f5a99f 100644
--- a/kernel/x86_emulate.c
+++ b/kernel/x86_emulate.c
@@ -1202,6 +1202,13 @@ static inline int writeback(struct x86_emulate_ctxt *ctxt,
 
 	switch (c->dst.type) {
 	case OP_REG:
+
+		if (!c->dst.ptr) {
+			printk("writeback: b %02x mordm %02x\n",
+			       c->b, c->modrm);
+			return 0;
+		}
+
 		/* The 4-byte case *is* correct:
 		 * in 64-bit mode we zero-extend.
 		 */