diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index f76b8c35f9..c8e364cc69 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -12999,7 +12999,7 @@ CustomGcodeSpecificConfigDef::CustomGcodeSpecificConfigDef()
 // Common Defs
     def = this->add("layer_num", coInt);
     def->label = L("Layer number");
-    def->tooltip = L("Index of the current layer. One-based (i.e. first layer is number 1).");
+    def->tooltip = L("Index of the current layer. Zero-based (i.e. first layer is number 0), except in extrusion role change G-code, where it is one-based.");
 
     def = this->add("layer_z", coFloat);
     def->label = L("Layer Z");