diff --git a/data/gui/window/unit_recall.cfg b/data/gui/window/unit_recall.cfg
index efff62a31e2..a3096f1d01d 100644
--- a/data/gui/window/unit_recall.cfg
+++ b/data/gui/window/unit_recall.cfg
@@ -339,6 +339,7 @@
 												id = "filter_box"
 												definition = "default"
 												{FILTER_TEXT_BOX_HINT}
+												tooltip = _ "Search for unit name, unit type name, or unit level."
 											[/text_box]
 
 										[/column]