diff --git a/lib/Slic3r/Config.pm b/lib/Slic3r/Config.pm
index ca6d5159..a48239ec 100644
--- a/lib/Slic3r/Config.pm
+++ b/lib/Slic3r/Config.pm
@@ -713,7 +713,7 @@ our $Options = {
     },
     'support_material_threshold' => {
         label   => 'Overhang threshold',
-        tooltip => 'Support material will not generated for overhangs whose slope angle is above the given threshold. Set to zero for automatic detection.',
+        tooltip => 'Support material will not generated for overhangs whose slope angle (90° = vertical) is above the given threshold. In other words, this value represent the most horizontal slope (measured from the horizontal plane) that you can print without support material. Set to zero for automatic detection (recommended).',
         sidetext => '°',
         scope   => 'object',
         category => 'Support material',