diff --git a/src/helpers/normalizeFiletype.ts b/src/helpers/normalizeFiletype.ts
index 9972b5d..f6aba73 100644
--- a/src/helpers/normalizeFiletype.ts
+++ b/src/helpers/normalizeFiletype.ts
@@ -1,35 +1,37 @@
-export const normalizeFiletype = (filetype: string): string => {
-  const lowercaseFiletype = filetype.toLowerCase();
-
-  switch (lowercaseFiletype) {
-    case "jfif":
-    case "jpg":
-      return "jpeg";
-    case "htm":
-      return "html";
-    case "tex":
-      return "latex";
-    case "md":
-      return "markdown";
-    default:
-      return lowercaseFiletype;
-  }
-};
-
-export const normalizeOutputFiletype = (filetype: string): string => {
-  const lowercaseFiletype = filetype.toLowerCase();
-
-  switch (lowercaseFiletype) {
-    case "jpeg":
-      return "jpg";
-    case "latex":
-      return "tex";
-    case "markdown_phpextra":
-    case "markdown_strict":
-    case "markdown_mmd":
-    case "markdown":
-      return "md";
-    default:
-      return lowercaseFiletype;
-  }
-};
+export const normalizeFiletype = (filetype: string): string => {
+  const lowercaseFiletype = filetype.toLowerCase();
+
+  switch (lowercaseFiletype) {
+    case "jfif":
+    case "jpg":
+      return "jpeg";
+    case "htm":
+      return "html";
+    case "tex":
+      return "latex";
+    case "md":
+      return "markdown";
+    case "unknown":
+      return "m4a";
+    default:
+      return lowercaseFiletype;
+  }
+};
+
+export const normalizeOutputFiletype = (filetype: string): string => {
+  const lowercaseFiletype = filetype.toLowerCase();
+
+  switch (lowercaseFiletype) {
+    case "jpeg":
+      return "jpg";
+    case "latex":
+      return "tex";
+    case "markdown_phpextra":
+    case "markdown_strict":
+    case "markdown_mmd":
+    case "markdown":
+      return "md";
+    default:
+      return lowercaseFiletype;
+  }
+};