diff --git a/package.nls.json b/package.nls.json
index f506322..b0ceaad 100644
--- a/package.nls.json
+++ b/package.nls.json
@@ -91,6 +91,7 @@
     "cph.submit.notKattis": "Not a kattis problem.",
     "cph.submit.notCodeforces": "Not a codeforces problem.",
     "cph.utils.unsupported": "Unsupported file extension. Only these types are valid: {0}",
+    "cph.utils.noActiveEditor": "No active editor found.",
     "cph.preferences.invalidSaveLocation": "Invalid save location, reverting to default. path not exists: {0}",
     "cph.processRunSingle.invalidChecker": "Custom checker script not found at '{0}'"
 }
diff --git a/package.nls.zh-cn.json b/package.nls.zh-cn.json
index d0a3497..ddf4b66 100644
--- a/package.nls.zh-cn.json
+++ b/package.nls.zh-cn.json
@@ -91,6 +91,7 @@
     "cph.submit.notKattis": "不是 Kattis 题目。",
     "cph.submit.notCodeforces": "不是 Codeforces 题目。",
     "cph.utils.unsupported": "不支持的文件扩展名。只有以下类型有效：{0}",
+    "cph.utils.noActiveEditor": "未发现活动中的编辑器。",
     "cph.preferences.invalidSaveLocation": "保存位置无效，正在恢复为默认值。路径不存在：{0}",
     "cph.processRunSingle.invalidChecker": "在“{0}”处未找到自定义判题脚本"
 }
diff --git a/src/utils.ts b/src/utils.ts
index 901cb37..16b4fa6 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -40,7 +40,7 @@ const oc = vscode.window.createOutputChannel('cph');
  * Get language based on file extension
  */
 export const getLanguage = (srcPath: string): Language => {
-    const extension = path.extname(srcPath).split('.').pop();
+    const extension = path.extname(srcPath).toLowerCase().replace('.', '');
     let langName: string | void = undefined;
     for (const [lang, ext] of Object.entries(config.extensions)) {
         if (ext === extension) {
@@ -48,6 +48,13 @@ export const getLanguage = (srcPath: string): Language => {
         }
     }
 
+    if (
+        langName === undefined &&
+        (config.extensions as any)[extension] !== undefined
+    ) {
+        langName = extension;
+    }
+
     if (langName === undefined) {
         throw new Error('Invalid extension');
     }
@@ -148,9 +155,8 @@ export const getLanguage = (srcPath: string): Language => {
 };
 
 export const isValidLanguage = (srcPath: string): boolean => {
-    return config.supportedExtensions.includes(
-        path.extname(srcPath).split('.')[1],
-    );
+    const ext = path.extname(srcPath).toLowerCase().replace('.', '');
+    return config.supportedExtensions.includes(ext);
 };
 
 export const isCodeforcesUrl = (url: URL): boolean => {
@@ -194,6 +200,12 @@ export const randomId = (index: number | null) => {
  * unsupported.
  */
 export const checkUnsupported = (srcPath: string): boolean => {
+    if (srcPath === '') {
+        vscode.window.showErrorMessage(
+            localize('cph.utils.noActiveEditor', 'No active editor found.'),
+        );
+        return true;
+    }
     if (!isValidLanguage(srcPath)) {
         vscode.window.showErrorMessage(
             localize(