diff --git a/src/sed/Makefile.kmk b/src/sed/Makefile.kmk
index f34b3e8..1734c59 100644
--- a/src/sed/Makefile.kmk
+++ b/src/sed/Makefile.kmk
@@ -57,6 +57,7 @@ kmk_sed_SOURCES = \
 	sed/mbcs.c \
 	lib/getopt1.c \
 	lib/getopt.c \
+	lib/obstack.c \
 	lib/utils.c
 kmk_sed_SOURCES.darwin = \
 	lib/strverscmp.c \