diff --git a/server.go b/server.go
index d4dac2c5a..9253a930f 100644
--- a/server.go
+++ b/server.go
@@ -428,6 +428,7 @@ func main() {
 					byteEntries, _ := json.MarshalIndent(dirEntries, "", " ")
 					writer.Write(byteEntries)
 				} else {
+					writer.Header().Set("Content-Type", "text/plain")
 					http.ServeFile(writer, request, filePath)
 				}
 			}