diff --git a/programs/x509/cert_write.c b/programs/x509/cert_write.c
index d36d73c..9a7dc59 100644
--- a/programs/x509/cert_write.c
+++ b/programs/x509/cert_write.c
@@ -507,7 +507,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_mpi_read_string "
-                        "returned -0x%04x - %s\n\n", -ret, buf );
+                        "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -527,7 +527,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509_crt_parse_file "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -537,7 +537,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509_dn_gets "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -561,7 +561,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509_csr_parse_file "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -571,7 +571,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509_dn_gets "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -596,7 +596,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_pk_parse_keyfile "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -612,7 +612,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_pk_parse_keyfile "
-                        "returned -x%02x - %s\n\n", -ret, buf );
+                        "returned -x%02x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -646,7 +646,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_subject_name "
-                        "returned -0x%04x - %s\n\n", -ret, buf );
+                        "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -654,7 +654,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_issuer_name "
-                        "returned -0x%04x - %s\n\n", -ret, buf );
+                        "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -669,7 +669,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_serial "
-                        "returned -0x%04x - %s\n\n", -ret, buf );
+                        "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -678,7 +678,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_validity "
-                        "returned -0x%04x - %s\n\n", -ret, buf );
+                        "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
         goto exit;
     }
 
@@ -696,7 +696,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  x509write_crt_set_basic_contraints "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -716,7 +716,7 @@
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_subject"
                             "_key_identifier returned -0x%04x - %s\n\n",
-                            -ret, buf );
+                            (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -735,7 +735,7 @@
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_authority_"
                             "key_identifier returned -0x%04x - %s\n\n",
-                            -ret, buf );
+                            (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -754,7 +754,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_key_usage "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -772,7 +772,7 @@
         {
             mbedtls_strerror( ret, buf, 1024 );
             mbedtls_printf( " failed\n  !  mbedtls_x509write_crt_set_ns_cert_type "
-                            "returned -0x%04x - %s\n\n", -ret, buf );
+                            "returned -0x%04x - %s\n\n", (unsigned int) -ret, buf );
             goto exit;
         }
 
@@ -790,7 +790,7 @@
     {
         mbedtls_strerror( ret, buf, 1024 );
         mbedtls_printf( " failed\n  !  write_certificate -0x%04x - %s\n\n",
-                        -ret, buf );
+                        (unsigned int) -ret, buf );
         goto exit;
     }