diff --git a/src/isomorphic/classic/types/checkReactTypeSpec.js b/src/isomorphic/classic/types/checkReactTypeSpec.js
index a5aa145940f45..104f69dc4422e 100644
--- a/src/isomorphic/classic/types/checkReactTypeSpec.js
+++ b/src/isomorphic/classic/types/checkReactTypeSpec.js
@@ -88,8 +88,8 @@ function checkReactTypeSpec(typeSpecs, values, location, componentName, element,
           componentStackInfo
         );
       }
-      if (mismatched.includes(typeSpecName.toLowerCase())) {
-        const mismatch = mismatched.find(item => item === typeSpecName.toLowerCase());
+      if (mismatched.indexOf(typeSpecName.toLowerCase()) !== -1) {
+        const mismatch = mismatched[mismatched.indexOf(typeSpecName.toLowerCase())];
         warning(
           false,
           'Provided prop %s is not defined in propTypes, did you mean %s?',