diff --git a/programs/pkey/ecdsa.c b/programs/pkey/ecdsa.c
index 3cba7e8..0783c71 100644
--- a/programs/pkey/ecdsa.c
+++ b/programs/pkey/ecdsa.c
@@ -162,7 +162,7 @@
         printf( " failed\n  ! ecdsa_genkey returned %d\n", ret );
         goto exit;
     }
-    printf( " ok (signature length = %zu)\n", sig_len );
+    printf( " ok (signature length = %u)\n", sig_len );
 
     dump_buf( "  + Hash: ", hash, sizeof hash );
     dump_buf( "  + Signature: ", sig, sig_len );