diff --git a/include/fc/crypto/sha256.hpp b/include/fc/crypto/sha256.hpp
index 00c726b..af0e6b2 100644
--- a/include/fc/crypto/sha256.hpp
+++ b/include/fc/crypto/sha256.hpp
@@ -83,8 +83,6 @@ class sha256
 } // fc
 namespace std
 {
-    template<typename T> struct hash;
-
     template<>
     struct hash<fc::sha256>
     {