diff --git a/dist/tools/zep_dispatch/main.c b/dist/tools/zep_dispatch/main.c
index 6efac625e5..3dcc62f54d 100644
--- a/dist/tools/zep_dispatch/main.c
+++ b/dist/tools/zep_dispatch/main.c
@@ -105,7 +105,7 @@ static void dispatch_loop(int sock, dispatch_cb_t dispatch, void *ctx)
 }
 
 static topology_t topology;
-static const char *graphviz_file;
+static const char *graphviz_file = "example.gv";
 static void _info_handler(int signal)
 {
     if (signal != SIGUSR1) {
diff --git a/dist/tools/zep_dispatch/topology.c b/dist/tools/zep_dispatch/topology.c
index 1744ba0229..173f1fdb63 100644
--- a/dist/tools/zep_dispatch/topology.c
+++ b/dist/tools/zep_dispatch/topology.c
@@ -151,10 +151,14 @@ int topology_print(const char *file, const topology_t *t)
 
     for (list_node_t *edge = t->edges.next; edge; edge = edge->next) {
         struct edge *super = container_of(edge, struct edge, next);
-        fprintf(out, "\t%s -> %s [ label = \"%.2f\" ]\n",
-                super->a->name, super->b->name, super->weight_a_b);
-        fprintf(out, "\t%s -> %s [ label = \"%.2f\" ]\n",
-                super->b->name, super->a->name, super->weight_b_a);
+        if (super->weight_a_b) {
+            fprintf(out, "\t%s -> %s [ label = \"%.2f\" ]\n",
+                    super->a->name, super->b->name, super->weight_a_b);
+        }
+        if (super->weight_b_a) {
+            fprintf(out, "\t%s -> %s [ label = \"%.2f\" ]\n",
+                    super->b->name, super->a->name, super->weight_b_a);
+        }
     }
 
     fprintf(out, "}\n");