diff --git a/xs/src/libslic3r/PrintConfig.cpp b/xs/src/libslic3r/PrintConfig.cpp
index 9be29718d..ccf9ccc7e 100644
--- a/xs/src/libslic3r/PrintConfig.cpp
+++ b/xs/src/libslic3r/PrintConfig.cpp
@@ -578,7 +578,7 @@ PrintConfigDef::PrintConfigDef()
         def->default_value = opt;
     }
     
-    def = this->add("gap_fill_speed", coFloat);
+    def = this->add("gap_fill_speed", coFloatOrPercent);
     def->label = "↳ gaps";
     def->full_label = "Gap fill speed";
     def->gui_type = "f_enum_open";
@@ -590,7 +590,7 @@ PrintConfigDef::PrintConfigDef()
     def->min = 0;
     def->enum_values.push_back("0");
     def->enum_labels.push_back("auto");
-    def->default_value = new ConfigOptionFloat(20);
+    def->default_value = new ConfigOptionFloatOrPercent(20);
 
     def = this->add("gcode_arcs", coBool);
     def->label = "Use native G-code arcs";
diff --git a/xs/src/libslic3r/PrintConfig.hpp b/xs/src/libslic3r/PrintConfig.hpp
index ce5162ffa..856e5def1 100644
--- a/xs/src/libslic3r/PrintConfig.hpp
+++ b/xs/src/libslic3r/PrintConfig.hpp
@@ -219,7 +219,7 @@ class PrintRegionConfig : public virtual StaticPrintConfig
     ConfigOptionPercent             fill_density;
     ConfigOptionBool                fill_gaps;
     ConfigOptionEnum<InfillPattern> fill_pattern;
-    ConfigOptionFloat               gap_fill_speed;
+    ConfigOptionFloatOrPercent      gap_fill_speed;
     ConfigOptionInt                 infill_extruder;
     ConfigOptionFloatOrPercent      infill_extrusion_width;
     ConfigOptionInt                 infill_every_layers;