diff --git a/src/index.js b/src/index.js
index 7017b7a..40259e6 100644
--- a/src/index.js
+++ b/src/index.js
@@ -12,7 +12,7 @@ export function isFSA(action) {
 }
 
 export function isError(action) {
-  return action.error === true;
+  return isFSA(action) && action.error === true;
 }
 
 function isValidKey(key) {