diff --git a/server.c b/server.c
index c1ced42..7c4804a 100644
--- a/server.c
+++ b/server.c
@@ -183,8 +183,12 @@
 
 		if (first)
 			memcpy(cmdret, &cmd, sizeof(cmd));
-		else
-			assert(cmdret->opcode == cmd.opcode);
+		else if (cmdret->opcode != cmd.opcode) {
+			log_err("fio: fragment opcode mismatch (%d != %d)\n",
+					cmdret->opcode, cmd.opcode);
+			ret = 1;
+			break;
+		}
 
 		if (!cmd.pdu_len)
 			break;