diff --git a/Makefile b/Makefile
index 581d2a1..5e2c70d 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ PREFIX_N != (test -d $(PREFIX) && [ '-' != $(PREFIX) ] \
 	&& CDPATH= cd -P -- $(PREFIX) && pwd -P)
 MANDIR != [ $(PREFIX_N) = / ] && printf '/usr/share/man\n' \
 	|| printf '/share/man\n'
-SYSEXITS != printf '\043include <sysexits.h>\n' | cpp -M - | sed 's/ /\n/g' \
+SYSEXITS != printf '\043include <sysexits.h>\n' | cpp -M - | tr ' ' '\n' \
 	| sed -n 's/sysexits\.h//p' || printf 'include\n'
 
 CC ?= cc