diff --git a/src/slic3r/GUI/GUI_App.cpp b/src/slic3r/GUI/GUI_App.cpp
index bbba1d93ba..97e78798f5 100644
--- a/src/slic3r/GUI/GUI_App.cpp
+++ b/src/slic3r/GUI/GUI_App.cpp
@@ -43,7 +43,7 @@ namespace GUI {
 
 wxString file_wildcards(FileType file_type, const std::string &custom_extension)
 {
-    static const wxString defaults[FT_SIZE] = {
+    static const std::string defaults[FT_SIZE] = {
         /* FT_STL */   "STL files (*.stl)|*.stl;*.STL",
         /* FT_OBJ */   "OBJ files (*.obj)|*.obj;*.OBJ",
         /* FT_AMF */   "AMF files (*.amf)|*.zip.amf;*.amf;*.AMF;*.xml;*.XML",
@@ -57,13 +57,17 @@ wxString file_wildcards(FileType file_type, const std::string &custom_extension)
         /* FT_PNGZIP */"Zipped PNG files (*.zip)|*.zip;*.ZIP",    // This is lame, but that's what we use for SLA
     };
 
-    wxString out = defaults[file_type];
+	std::string out = defaults[file_type];
     if (! custom_extension.empty()) {
-        // Append the custom extension to the wildcards, so that the file dialog would not add the default extension to it.
-        out += ";*";
-        out += from_u8(custom_extension);
+        // Find the custom extension in the template.
+        if (out.find(std::string("*") + custom_extension + ",") == std::string::npos && out.find(std::string("*") + custom_extension + ")") == std::string::npos) {
+            // The custom extension was not found in the template.
+            // Append the custom extension to the wildcards, so that the file dialog would not add the default extension to it.
+			boost::replace_first(out, ")|", std::string(", *") + custom_extension + ")|");
+			out += std::string(";*") + custom_extension;
+        }
     }
-    return out;
+	return wxString::FromUTF8(out.c_str());
 }
 
 static std::string libslic3r_translate_callback(const char *s) { return wxGetTranslation(wxString(s, wxConvUTF8)).utf8_str().data(); }