diff --git a/apps/api-extractor/src/api/ExtractorConfig.ts b/apps/api-extractor/src/api/ExtractorConfig.ts
index 5392defc70e..57970d4f773 100644
--- a/apps/api-extractor/src/api/ExtractorConfig.ts
+++ b/apps/api-extractor/src/api/ExtractorConfig.ts
@@ -210,7 +210,7 @@ export class ExtractorConfig {
     path.join(__dirname, '../schemas/api-extractor-defaults.json')
   );
 
-  private static readonly _declarationFileExtensionRegExp: RegExp = /\.d\.ts$/i;
+  private static readonly _declarationFileExtensionRegExp: RegExp = /\.d\.(c|m)?ts$/i;
 
   /** {@inheritDoc IConfigFile.projectFolder} */
   public readonly projectFolder: string;
diff --git a/common/changes/@microsoft/api-extractor/main_2023-03-20-14-36.json b/common/changes/@microsoft/api-extractor/main_2023-03-20-14-36.json
new file mode 100644
index 00000000000..49ee142c6f1
--- /dev/null
+++ b/common/changes/@microsoft/api-extractor/main_2023-03-20-14-36.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/api-extractor",
+      "comment": "Add api-extractor support for .d.mts and .d.cts files",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@microsoft/api-extractor"
+}
\ No newline at end of file