diff --git a/ChangeLog b/ChangeLog
index 252c25c0fb..50da0310bf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2017-12-11  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* string/Makefile (CFLAGS-inl-tester.c): Replace = with +=.
+	(CFLAGS-noinl-tester.c): Likewise.
+	(CFLAGS-tst-strlen.c): Likewise.
+	(CFLAGS-stratcliff.c): Likewise.
+	(CFLAGS-test-ffs.c): Likewise.
+	(CFLAGS-tst-inlcall.c): Likewise.
+	(CFLAGS-tst-xbzero-opt.c): Likewise.
+	(CFLAGS-memcpy.c): Likewise.
+	(CFLAGS-wordcopy.c): Likewise.
+
 2017-12-11  Stefan Liebler  <stli@linux.vnet.ibm.com>
 
 	* sysdeps/s390/s390-64/dl-trampoline.h (_dl_runtime_resolve):
diff --git a/string/Makefile b/string/Makefile
index d7e90a38a5..74ba4f2f76 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -69,13 +69,13 @@ endif
 
 include ../Rules
 
-CFLAGS-inl-tester.c = -fno-builtin
-CFLAGS-noinl-tester.c = -fno-builtin
-CFLAGS-tst-strlen.c = -fno-builtin
-CFLAGS-stratcliff.c = -fno-builtin
-CFLAGS-test-ffs.c = -fno-builtin
-CFLAGS-tst-inlcall.c = -fno-builtin
-CFLAGS-tst-xbzero-opt.c = -O3
+CFLAGS-inl-tester.c += -fno-builtin
+CFLAGS-noinl-tester.c += -fno-builtin
+CFLAGS-tst-strlen.c += -fno-builtin
+CFLAGS-stratcliff.c += -fno-builtin
+CFLAGS-test-ffs.c += -fno-builtin
+CFLAGS-tst-inlcall.c += -fno-builtin
+CFLAGS-tst-xbzero-opt.c += -O3
 # BZ 21006: Resolve all functions but at least explicit_bzero at startup.
 # Otherwise the test fails on s390x as the memcpy in prepare_test_buffer is
 # done by loading r4 / r5 with the test_pattern and using store multiple
@@ -86,8 +86,8 @@ CFLAGS-tst-xbzero-opt.c = -O3
 LDFLAGS-tst-xbzero-opt = -z now
 
 # Called during TLS initialization.
-CFLAGS-memcpy.c = $(no-stack-protector)
-CFLAGS-wordcopy.c = $(no-stack-protector)
+CFLAGS-memcpy.c += $(no-stack-protector)
+CFLAGS-wordcopy.c += $(no-stack-protector)
 
 ifeq ($(run-built-tests),yes)
 $(objpfx)tst-svc-cmp.out: tst-svc.expect $(objpfx)tst-svc.out