diff --git a/Makefile.in b/Makefile.in
index c233d3dd..36069013 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -132,10 +132,10 @@ ifdef C
 	# don't use FORTIFY with sparse because glibc with FORTIFY can
 	# generate so many sparse errors that sparse stops parsing,
 	# which masks real errors that we want to see.
+	CFLAGS += -U_FORTIFY_SOURCE
 else
 	check = true
 	check_echo = true
-	CFLAGS += -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2
 endif
 
 %.o.d: %.c
diff --git a/configure.ac b/configure.ac
index d059e1c7..0692d5a8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8,7 +8,7 @@ LIBBTRFS_MAJOR=0
 LIBBTRFS_MINOR=1
 LIBBTRFS_PATCHLEVEL=1
 
-CFLAGS=${CFLAGS:-"-g -O1 -Wall"}
+CFLAGS=${CFLAGS:-"-g -O1 -Wall -D_FORTIFY_SOURCE=2"}
 AC_SUBST([CFLAGS])
 
 AC_PREREQ([2.60])