diff --git a/src/config.c b/src/config.c
index 9fa85599..8040adc2 100644
--- a/src/config.c
+++ b/src/config.c
@@ -438,6 +438,12 @@ void loadServerConfigFromString(char *config) {
         sdsfreesplitres(argv,argc);
     }
     sdsfreesplitres(lines,totlines);
+
+    /* Sanity checks. */
+    if (server.cluster_enabled && server.masterhost) {
+        err = "slaveof directive not allowed in cluster mode";
+        goto loaderr;
+    }
     return;
 
 loaderr: