diff --git a/third_party/microtar/src/microtar.c b/third_party/microtar/src/microtar.c
index 4b8977600..a3c67c70f 100644
--- a/third_party/microtar/src/microtar.c
+++ b/third_party/microtar/src/microtar.c
@@ -187,7 +187,7 @@ int mtar_open(mtar_t *tar, const char *filename, const char *mode) {
 
   /* Assure mode is always binary */
   if ( strchr(mode, 'r') ) mode = "rb";
-  if ( strchr(mode, 'w') ) mode = "wb";
+  if ( strchr(mode, 'w') ) mode = "w+b";
   if ( strchr(mode, 'a') ) mode = "ab";
   /* Open file */
   tar->stream = fopen(filename, mode);