diff --git a/luigi/requirements.txt b/luigi/requirements.txt
old mode 100755
new mode 100644
index 74dca85..836150e
--- a/luigi/requirements.txt
+++ b/luigi/requirements.txt
@@ -58,7 +58,7 @@ Pillow==4.3.0
 pox==0.2.3
 ppft==1.6.4.7.1
 prompt-toolkit==1.0.15
-protobuf==3.5.1
+protobuf==3.15.0
 ptyprocess==0.5.2
 pycairo==1.15.4
 pycrypto==2.6.1