diff --git a/img/Makefile b/img/Makefile
index 0e5aa0d..ed5acc2 100644
--- a/img/Makefile
+++ b/img/Makefile
@@ -1,4 +1,4 @@
-dotfiles = $(shell ls *.dot | sed 's/\.dot/\.pdf/' -)
+dotfiles = $(shell ls *.dot | sed -e 's/\.dot/\.pdf/')
 
 all: $(dotfiles)