diff --git a/glog_file.go b/glog_file.go
index 1a1ed66..8dcb2bc 100644
--- a/glog_file.go
+++ b/glog_file.go
@@ -64,6 +64,9 @@
 	if err == nil {
 		userName = current.Username
 	}
+
+	// Sanitize userName since it may contain filepath separators on Windows.
+	userName = strings.Replace(userName, `\`, "_", -1)
 }
 
 // shortHostname returns its argument, truncating at the first period.