diff --git a/library/sha512.c b/library/sha512.c
index ed044ed..5decc8f 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -757,7 +757,7 @@
 
         if( j == 5 || j == 6 )
         {
-            memset( buf, '\xAA', buflen = 131 );
+            memset( buf, 0xAA, buflen = 131 );
             sha512_hmac_starts( &ctx, buf, buflen, k );
         }
         else