diff --git a/tools/mapmerge2/requirements.txt b/tools/mapmerge2/requirements.txt
index 46d0fa64c5..095843b2d2 100644
--- a/tools/mapmerge2/requirements.txt
+++ b/tools/mapmerge2/requirements.txt
@@ -1,3 +1,3 @@
 pygit2==0.26.0
 bidict==0.13.1
-Pillow=5.1.0
+Pillow==5.1.0