diff --git a/programs/x509/cert_app.c b/programs/x509/cert_app.c
index 3f50a7a14..c6434fe1f 100644
--- a/programs/x509/cert_app.c
+++ b/programs/x509/cert_app.c
@@ -57,6 +57,7 @@ int main( void )
 #include "mbedtls/net.h"
 #include "mbedtls/ssl.h"
 #include "mbedtls/x509.h"
+#include "mbedtls/debug.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -380,6 +381,10 @@ int main( int argc, char *argv[] )
 
         mbedtls_printf( " ok\n" );
 
+#if defined(MBEDTLS_DEBUG_C)
+        mbedtls_debug_set_threshold( opt.debug_level );
+#endif
+
         /*
          * 2. Start the connection
          */