diff --git a/types/mem-cache/tsconfig.json b/types/mem-cache/tsconfig.json
index 9587e02f72..3c3a2e701a 100644
--- a/types/mem-cache/tsconfig.json
+++ b/types/mem-cache/tsconfig.json
@@ -7,6 +7,7 @@
         "noImplicitAny": true,
         "noImplicitThis": true,
         "strictNullChecks": true,
+        "strictFunctionTypes": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"