diff --git a/doc/Makefile.am b/doc/Makefile.am
index 9141ab2..670aa54 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -123,7 +123,7 @@
 edit_sgml_SOURCES =	\
 	edit-sgml.c	\
 	$(NULL)
-edit_sgml_CC = $(CC_FOR_BUILD)
+edit_sgml_CC := $(CC_FOR_BUILD)
 #
 check_SCRIPTS =			\
 	check-missing-doc	\