diff --git a/src/stratifier.c b/src/stratifier.c
index 8281fa0..47d0fed 100644
--- a/src/stratifier.c
+++ b/src/stratifier.c
@@ -6004,7 +6004,30 @@ static void check_best_diff(sdata_t *sdata, user_instance_t *user,worker_instanc
 	stratum_send_message(sdata, client, buf);
 }
 
-#define JSON_ERR(err) json_string(SHARE_ERR(err))
+/* Map ckpool's share_err enum to standard Stratum mining v1 error codes
+ * (per the Slush stratum spec). Miners like AxeOS / Bitaxe expect the
+ * "error" field on a share response to be a [code, message, traceback]
+ * array; without this they show "unknown error" because cJSON_IsArray
+ * returns false on a bare string. */
+static inline int share_err_code(enum share_err err)
+{
+	switch (err) {
+	case SE_STALE:
+	case SE_INVALID_JOBID:
+	case SE_NTIME_INVALID:
+		return 21; /* job not found / stale */
+	case SE_DUPE:
+		return 22; /* duplicate share */
+	case SE_HIGH_DIFF:
+		return 23; /* low difficulty share */
+	case SE_NO_USERNAME:
+		return 24; /* unauthorized worker */
+	default:
+		return 20; /* other / unknown */
+	}
+}
+
+#define JSON_ERR(err) json_pack("[isn]", share_err_code(err), SHARE_ERR(err))
 
 /* Needs to be entered with client holding a ref count. */
 static json_t *parse_submit(stratum_instance_t *client, json_t *json_msg,