diff --git a/types/gm/gm-tests.ts b/types/gm/gm-tests.ts
index b22b7ffbc5..ecc8104ec6 100644
--- a/types/gm/gm-tests.ts
+++ b/types/gm/gm-tests.ts
@@ -66,6 +66,7 @@ declare const defineValue: string;
 declare const customCommand: string;
 declare const customInArguments: string[];
 declare const customOutArguments: string[];
+declare const customFormat: string;
 let readStream: stream.PassThrough;
 
 gm(src)
@@ -309,6 +310,8 @@ gm(src)
 	})
 	.identify((err, info) => {
 	})
+	.identify(customFormat, (err, info) => {
+	})
 	.identify({ bufferStream: true }, (err, info) => {
 	})
 	.res((err, resolution) => {
diff --git a/types/gm/index.d.ts b/types/gm/index.d.ts
index 9fe2013913..5a5370e05b 100644
--- a/types/gm/index.d.ts
+++ b/types/gm/index.d.ts
@@ -3,6 +3,7 @@
 // Definitions by:  Joel Spadin <https://github.com/ChaosinaCan>
 //                  Maarten van Vliet <https://github.com/maartenvanvliet>
 //                  Vaclav Mlejnsky <https://github.com/mlejva>
+//                  Dimitry Kooijmans <https://github.com/mrcageman>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 /// <reference types="node"/>
@@ -284,6 +285,7 @@ declare namespace m {
         format(callback: GetterCallback<string>): State;
         format(opts: GetterOptions, callback: GetterCallback<string>): State;
         identify(callback: GetterCallback<ImageInfo>): State;
+        identify(format: string, callback: GetterCallback<string>): State;
         identify(opts: GetterOptions, callback: GetterCallback<ImageInfo>): State;
         res(callback: GetterCallback<string>): State;
         res(opts: GetterOptions, callback: GetterCallback<string>): State;