diff --git a/library/x509.c b/library/x509.c
index c451332..4c2f721 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -870,7 +870,7 @@
         ret = mbedtls_snprintf( p, n, " (%s, MGF1-%s, 0x%02X)",
                               md_info ? mbedtls_md_get_name( md_info ) : "???",
                               mgf_md_info ? mbedtls_md_get_name( mgf_md_info ) : "???",
-                              pss_opts->expected_salt_len );
+                              (unsigned int) pss_opts->expected_salt_len );
         MBEDTLS_X509_SAFE_SNPRINTF;
     }
 #else