Index: lib/sanitizer_common/sanitizer_posix.cc
===================================================================
--- lib/sanitizer_common/sanitizer_posix.cc
+++ lib/sanitizer_common/sanitizer_posix.cc
@@ -160,7 +160,7 @@
   int flags;
   switch (mode) {
     case RdOnly: flags = O_RDONLY; break;
-    case WrOnly: flags = O_WRONLY | O_CREAT; break;
+    case WrOnly: flags = O_WRONLY | O_CREAT | O_TRUNC; break;
     case RdWr: flags = O_RDWR | O_CREAT; break;
   }
   fd_t res = internal_open(filename, flags, 0660);