diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index 6e900ca1b4..6d52484e9c 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -310,7 +310,8 @@ void PrintConfigDef::init_common_params()
 
     def = this->add("thumbnails", coString);
     def->label = L("G-code thumbnails");
-    def->tooltip = L("Picture sizes to be stored into a .gcode / .bgcode and .sl1 / .sl1s files, in the following format: \"XxY/EXT, XxY/EXT, ...\"");
+    def->tooltip = L("Picture sizes to be stored into a .gcode / .bgcode and .sl1 / .sl1s files, in the following format: \"XxY/EXT, XxY/EXT, ...\"\n"
+                     "Currently supported extensions are PNG, QOI and JPG.");
     def->mode = comExpert;
     def->gui_type = ConfigOptionDef::GUIType::one_string;
     def->set_default_value(new ConfigOptionString());