diff --git a/src/ext/modelist.js b/src/ext/modelist.js
index d9b931c168..07092bb140 100644
--- a/src/ext/modelist.js
+++ b/src/ext/modelist.js
@@ -48,6 +48,7 @@ class Mode {
 
     /**
      * @param {string} filename
+     * @returns {RegExpMatchArray | null}
      */
     supportsFile(filename) {
         return filename.match(this.extRe);
diff --git a/types/ace-ext.d.ts b/types/ace-ext.d.ts
index 8393fb89b1..579d38c5e4 100644
--- a/types/ace-ext.d.ts
+++ b/types/ace-ext.d.ts
@@ -400,7 +400,7 @@ declare module "ace-code/src/ext/modelist" {
         mode: string;
         extensions: string;
         extRe: RegExp;
-        supportsFile(filename: string): RegExpMatchArray;
+        supportsFile(filename: string): RegExpMatchArray | null;
     }
 }
 declare module "ace-code/src/ext/themelist" {