diff --git a/makefile b/makefile
index 12d89b6..4dcd56b 100644
--- a/makefile
+++ b/makefile
@@ -78,7 +78,7 @@ GIT_HEAD_REV = $(shell git rev-parse --short HEAD)
 DOCKER_IMAGE_VERSION = $(shell date -u +'%Y%m%dt%H%M%S')_$(GIT_HEAD_REV)
 
 
-MAX_LINE_LEN = $(shell grep 'max-line-length = 100' setup.cfg | grep -oE "[0-9]+")
+MAX_LINE_LEN = $(shell grep 'max-line-length' setup.cfg | sed 's/[^0-9]\+//')
 
 
 build/envs.txt: requirements/conda.txt