diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index 69d06af48..aaff26f48 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -131,6 +131,7 @@ static int getrandom_wrapper( void *buf, size_t buflen, unsigned int flags )
 
 static int sysctl_arnd_wrapper( void *buf, size_t buflen )
 {
+    unsigned char *output = buf;
     int name[2];
     size_t len;
 
@@ -140,10 +141,10 @@ static int sysctl_arnd_wrapper( void *buf, size_t buflen )
     while( buflen > 0 )
     {
         len = buflen > 256 ? 256 : buflen;
-        if( sysctl(name, 2, buf, &len, NULL, 0) == -1 )
+        if( sysctl(name, 2, output, &len, NULL, 0) == -1 )
             return( -1 );
         buflen -= len;
-        buf += len;
+        output += len;
     }
     return( 0 );
 }