diff --git a/plugins/docker/docker_ b/plugins/docker/docker_
index 51d35865..8a05ccaf 100755
--- a/plugins/docker/docker_
+++ b/plugins/docker/docker_
@@ -453,9 +453,9 @@ def volumes(client, mode):
         )
 
         print('volumes_quantity.value', len(volumes))
-        print('volumes_quantity.extinfo', ', '.join(volume_summary(v) for v in volumes))
+        print('volumes_quantity.extinfo', (', '.join(volume_summary(v) for v in volumes)) or '-')
         print('dangling_quantity.value', len(dangling))
-        print('dangling_quantity.extinfo', ', '.join(volume_summary(i) for i in dangling))
+        print('dangling_quantity.extinfo', (', '.join(volume_summary(i) for i in dangling)) or '-')
 
 
 def size(client, mode):