diff --git a/programs/ssl/ssl_context_info.c b/programs/ssl/ssl_context_info.c
index 7ac01d6df3..7018080d4a 100644
--- a/programs/ssl/ssl_context_info.c
+++ b/programs/ssl/ssl_context_info.c
@@ -22,6 +22,7 @@
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif
+#include "mbedtls/debug.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -164,6 +165,7 @@ void printf_dbg( const char *str, ... )
     }
 }
 
+MBEDTLS_PRINTF_ATTRIBUTE( 1, 2 )
 void printf_err( const char *str, ... )
 {
     va_list args;
@@ -470,7 +472,8 @@ size_t read_next_b64_code( uint8_t **b64, size_t *max_len )
             }
             else if( len > *max_len )
             {
-                printf_err( "The code found is too large by %u bytes.\n", len - *max_len );
+                printf_err( "The code found is too large by %" MBEDTLS_PRINTF_SIZET " bytes.\n",
+                            len - *max_len );
                 len = pad = 0;
             }
             else if( len % 4 != 0 )