diff --git a/ext/tag_edit/theme.php b/ext/tag_edit/theme.php
index 0332273b..1e9bf021 100644
--- a/ext/tag_edit/theme.php
+++ b/ext/tag_edit/theme.php
@@ -24,7 +24,7 @@ class TagEditTheme extends Themelet {
 		$html = make_form(make_link("tag_edit/mass_source_set"), "POST") . "
 				<input type='hidden' name='tags' value='$h_terms'>
 				<input type='text' name='source' value=''>
-				<input type='submit' value='Set Source For All'>
+				<input type='submit' value='Set Source For All' onclick='return confirm(\"This will mass-edit all sources on the page.\nAre you sure you want to do this?\")'>
 			</form>
 		";
 		return $html;