diff --git a/api/client/service/opts.go b/api/client/service/opts.go
index 640aaa0205..028d0887a5 100644
--- a/api/client/service/opts.go
+++ b/api/client/service/opts.go
@@ -217,7 +217,7 @@ func (m *MountOpt) Set(value string) error {
 			}
 			setValueOnMap(volumeOptions().DriverConfig.Options, value)
 		default:
-			return fmt.Errorf("unexpected key '%s' in '%s'", key, value)
+			return fmt.Errorf("unexpected key '%s' in '%s'", key, field)
 		}
 	}