diff --git a/programs/x509/cert_app.c b/programs/x509/cert_app.c
index 432eefb..7723a37 100644
--- a/programs/x509/cert_app.c
+++ b/programs/x509/cert_app.c
@@ -258,7 +258,7 @@
     {
         if( ( ret = mbedtls_x509_crt_parse_path( &cacert, opt.ca_path ) ) < 0 )
         {
-            mbedtls_printf( " failed\n  !  mbedtls_x509_crt_parse_path returned -0x%x\n\n", -ret );
+            mbedtls_printf( " failed\n  !  mbedtls_x509_crt_parse_path returned -0x%x\n\n", (unsigned int) -ret );
             goto exit;
         }
 
@@ -268,7 +268,7 @@
     {
         if( ( ret = mbedtls_x509_crt_parse_file( &cacert, opt.ca_file ) ) < 0 )
         {
-            mbedtls_printf( " failed\n  !  mbedtls_x509_crt_parse_file returned -0x%x\n\n", -ret );
+            mbedtls_printf( " failed\n  !  mbedtls_x509_crt_parse_file returned -0x%x\n\n", (unsigned int) -ret );
             goto exit;
         }
 
@@ -282,7 +282,7 @@
     {
         if( ( ret = mbedtls_x509_crl_parse_file( &cacrl, opt.crl_file ) ) != 0 )
         {
-            mbedtls_printf( " failed\n  !  mbedtls_x509_crl_parse returned -0x%x\n\n", -ret );
+            mbedtls_printf( " failed\n  !  mbedtls_x509_crl_parse returned -0x%x\n\n", (unsigned int) -ret );
             goto exit;
         }