diff --git a/library/x509_crt.c b/library/x509_crt.c
index f6879dd..5dc6568 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1097,7 +1097,7 @@
     WCHAR szDir[MAX_PATH];
     char filename[MAX_PATH];
     char *p;
-    int len = (int) strlen( path );
+    size_t len = strlen( path );
 
     WIN32_FIND_DATAW file_data;
     HANDLE hFind;
@@ -1131,7 +1131,7 @@
 
         w_ret = WideCharToMultiByte( CP_ACP, 0, file_data.cFileName,
                                      lstrlenW( file_data.cFileName ),
-                                     p, len - 1,
+                                     p, (int) len - 1,
                                      NULL, NULL );
         if( w_ret == 0 )
             return( MBEDTLS_ERR_X509_FILE_IO_ERROR );