diff --git a/types/concat-map/concat-map-tests.ts b/types/concat-map/concat-map-tests.ts
index e69de29bb2..9d99d221de 100644
--- a/types/concat-map/concat-map-tests.ts
+++ b/types/concat-map/concat-map-tests.ts
@@ -0,0 +1,8 @@
+import concatMap from "concat-map";
+
+const xs = [1, 2, 3, 4, 5, 6];
+concatMap(xs, x => (x % 2 ? [x - 0.1, x, x + 0.1] : []));
+// [0.9, 1, 1.1, 2.9, 3, 3.1, 4.9, 5, 5.1]
+
+concatMap(xs, x => x % 2);
+// [1, 0, 1, 0, 1, 0]
diff --git a/types/concat-map/index.d.ts b/types/concat-map/index.d.ts
index 4348c625a8..3e874a3449 100644
--- a/types/concat-map/index.d.ts
+++ b/types/concat-map/index.d.ts
@@ -1,15 +1,9 @@
 // Type definitions for concat-map 0.0
 // Project: https://github.com/substack/node-concat-map
-// Definitions by: My Self <https://github.com/me>
+// Definitions by: Claas Ahlrichs <https://github.com/claasahl>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.7
 
 export = concat_map;
 
-declare function concat_map(xs: any, fn: any): any;
-
-declare namespace concat_map {
-    const prototype: {
-    };
-
-}
-
+declare function concat_map<T, R>(xs: T[], fn: (x: T) => R | R[]): R[];
diff --git a/types/concat-map/tsconfig.json b/types/concat-map/tsconfig.json
index 8e84083a1f..5b6dcf9c5c 100644
--- a/types/concat-map/tsconfig.json
+++ b/types/concat-map/tsconfig.json
@@ -1,22 +1,17 @@
 {
     "compilerOptions": {
         "module": "commonjs",
-        "lib": [
-            "es6"
-        ],
+        "lib": ["es6"],
         "noImplicitAny": true,
         "noImplicitThis": true,
         "strictNullChecks": true,
+        "strictFunctionTypes": true,
         "baseUrl": "../",
-        "typeRoots": [
-            "../"
-        ],
+        "typeRoots": ["../"],
         "types": [],
         "noEmit": true,
-        "forceConsistentCasingInFileNames": true
+        "forceConsistentCasingInFileNames": true,
+        "esModuleInterop": true
     },
-    "files": [
-        "index.d.ts",
-        "concat-map-tests.ts"
-    ]
+    "files": ["index.d.ts", "concat-map-tests.ts"]
 }