diff --git a/library/x509_crt.c b/library/x509_crt.c
index a623c57..0aa4f4c 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1629,6 +1629,8 @@
     }
 #endif /* MBEDTLS_THREADING_C */
 
+    memset( &sb, 0, sizeof( sb ) );
+
     while( ( entry = readdir( dir ) ) != NULL )
     {
         snp_ret = mbedtls_snprintf( entry_name, sizeof entry_name,