diff --git a/src/PrusaSlicer.cpp b/src/PrusaSlicer.cpp
index f7350dace4..60f3a13218 100644
--- a/src/PrusaSlicer.cpp
+++ b/src/PrusaSlicer.cpp
@@ -150,15 +150,11 @@ int CLI::run(int argc, char **argv)
     }
 
     // Read input file(s) if any.
-    for (const std::string& file : m_input_files) {
-        std::string ext = boost::filesystem::path(file).extension().string();
-        if (ext == ".gcode" || ext == ".g") {
-            if (boost::filesystem::exists(file)) {
-                start_as_gcodeviewer = true;
-                break;
-            }
+    for (const std::string& file : m_input_files)
+        if (is_gcode_file(file) && boost::filesystem::exists(file)) {
+            start_as_gcodeviewer = true;
+            break;
         }
-    }
     if (!start_as_gcodeviewer) {
         for (const std::string& file : m_input_files) {
             if (!boost::filesystem::exists(file)) {
diff --git a/src/libslic3r/Config.cpp b/src/libslic3r/Config.cpp
index b6b496ae91..ea6c78f7ce 100644
--- a/src/libslic3r/Config.cpp
+++ b/src/libslic3r/Config.cpp
@@ -589,7 +589,7 @@ void ConfigBase::setenv_() const
 
 void ConfigBase::load(const std::string &file)
 {
-    if (boost::iends_with(file, ".gcode") || boost::iends_with(file, ".g"))
+    if (is_gcode_file(file))
         this->load_from_gcode_file(file);
     else
         this->load_from_ini(file);
diff --git a/src/libslic3r/PresetBundle.cpp b/src/libslic3r/PresetBundle.cpp
index 1f1d118662..b31ee66644 100644
--- a/src/libslic3r/PresetBundle.cpp
+++ b/src/libslic3r/PresetBundle.cpp
@@ -667,7 +667,7 @@ DynamicPrintConfig PresetBundle::full_sla_config() const
 // If the file is loaded successfully, its print / filament / printer profiles will be activated.
 void PresetBundle::load_config_file(const std::string &path)
 {
-	if (boost::iends_with(path, ".gcode") || boost::iends_with(path, ".g")) {
+	if (is_gcode_file(path)) {
 		DynamicPrintConfig config;
 		config.apply(FullPrintConfig::defaults());
         config.load_from_gcode_file(path);
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index 28976064be..b797c7c19f 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -90,6 +90,7 @@ extern CopyFileResult check_copy(const std::string& origin, const std::string& c
 extern bool is_plain_file(const boost::filesystem::directory_entry &path);
 extern bool is_ini_file(const boost::filesystem::directory_entry &path);
 extern bool is_idx_file(const boost::filesystem::directory_entry &path);
+extern bool is_gcode_file(const std::string &path);
 
 // File path / name / extension splitting utilities, working with UTF-8,
 // to be published to Perl.
diff --git a/src/libslic3r/utils.cpp b/src/libslic3r/utils.cpp
index 3c14169360..2a1d12c1da 100644
--- a/src/libslic3r/utils.cpp
+++ b/src/libslic3r/utils.cpp
@@ -522,6 +522,12 @@ bool is_idx_file(const boost::filesystem::directory_entry &dir_entry)
 	return is_plain_file(dir_entry) && strcasecmp(dir_entry.path().extension().string().c_str(), ".idx") == 0;
 }
 
+bool is_gcode_file(const std::string &path)
+{
+	return boost::iends_with(path, ".gcode") || boost::iends_with(path, ".gco") ||
+		   boost::iends_with(path, ".g")     || boost::iends_with(path, ".ngc");
+}
+
 } // namespace Slic3r
 
 #ifdef WIN32
diff --git a/src/slic3r/GUI/GUI_App.cpp b/src/slic3r/GUI/GUI_App.cpp
index ef25651088..5de7af5d01 100644
--- a/src/slic3r/GUI/GUI_App.cpp
+++ b/src/slic3r/GUI/GUI_App.cpp
@@ -1866,11 +1866,9 @@ bool GUI_App::OnExceptionInMainLoop()
 void GUI_App::OSXStoreOpenFiles(const wxArrayString &fileNames)
 {
     size_t num_gcodes = 0;
-    for (const wxString &filename : fileNames) {
-        wxString fn = filename.Upper();
-        if (fn.EndsWith(".G") || fn.EndsWith(".GCODE"))
+    for (const wxString &filename : fileNames)
+        if (is_gcode_file(into_u8(filename)))
             ++ num_gcodes;
-    }
     if (fileNames.size() == num_gcodes) {
         // Opening PrusaSlicer by drag & dropping a G-Code onto PrusaSlicer icon in Finder,
         // just G-codes were passed. Switch to G-code viewer mode.
@@ -1890,8 +1888,7 @@ void GUI_App::MacOpenFiles(const wxArrayString &fileNames)
     std::vector<wxString>    gcode_files;
     std::vector<wxString>    non_gcode_files;
     for (const auto& filename : fileNames) {
-        wxString fn = filename.Upper();
-        if (fn.EndsWith(".G") || fn.EndsWith(".GCODE"))
+        if (is_gcode_file(into_u8(filename)))
             gcode_files.emplace_back(filename);
         else {
             files.emplace_back(into_u8(filename));
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index cb70666307..7824dcfdff 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -4847,9 +4847,7 @@ void Plater::load_gcode()
 
 void Plater::load_gcode(const wxString& filename)
 {
-    if (filename.empty() ||
-        (!filename.Lower().EndsWith(".gcode") && !filename.Lower().EndsWith(".g")) ||
-        m_last_loaded_gcode == filename)
+    if (! is_gcode_file(into_u8(filename)) || m_last_loaded_gcode == filename)
         return;
 
     m_last_loaded_gcode = filename;