diff --git a/programs/pkey/dh_server.c b/programs/pkey/dh_server.c
index 8bf2b1b..daa96e6 100644
--- a/programs/pkey/dh_server.c
+++ b/programs/pkey/dh_server.c
@@ -203,7 +203,11 @@
     /*
      * 5. Sign the parameters and send them
      */
-    mbedtls_sha1( buf, n, hash );
+    if( ( ret = mbedtls_sha1_ext( buf, n, hash ) ) != 0 )
+    {
+        mbedtls_printf( " failed\n  ! mbedtls_sha1_ext returned %d\n\n", ret );
+        goto exit;
+    }
 
     buf[n    ] = (unsigned char)( rsa.len >> 8 );
     buf[n + 1] = (unsigned char)( rsa.len      );