diff --git a/main/src/ui/util/helper.vala b/main/src/ui/util/helper.vala
index ecf0ab25..485e469f 100644
--- a/main/src/ui/util/helper.vala
+++ b/main/src/ui/util/helper.vala
@@ -445,7 +445,7 @@ public Widget? widget_if_tooltips_active(Widget w) {
     return use_tooltips() ? w : null;
 }
 
-public string? string_if_tooltips_active(string s) {
+public string? string_if_tooltips_active(string? s) {
     return use_tooltips() ? s : null;
 }