diff --git a/src/key.cpp b/src/key.cpp
index 71b2a868..3b88b69e 100644
--- a/src/key.cpp
+++ b/src/key.cpp
@@ -596,7 +596,7 @@ public:
 #ifdef DEBUG_ECIES
                 printf("The authentication code was invalid! The ciphered data has been corrupted!\n");
 #endif
-                return NULL;
+                return false;
         }
 
         // Create a buffer to hold the result.