Save makefile var clobbering
diff --git a/Makefile b/Makefile
index 4aacb99..f5d45f5 100644
--- a/Makefile
+++ b/Makefile
@@ -178,6 +178,10 @@
DEFINES += $(DEFINES_$(CONFIG)) INSTALL_PREFIX=\"$(prefix)\"
LDFLAGS += $(LDFLAGS_$(CONFIG))
+ifdef EXTRA_DEFINES
+DEFINES += EXTRA_DEFINES
+endif
+
CFLAGS += -std=c89 -pedantic
ifeq ($(HAS_CXX11),true)
CXXFLAGS += -std=c++11
diff --git a/templates/Makefile.template b/templates/Makefile.template
index caac503..0413f19 100644
--- a/templates/Makefile.template
+++ b/templates/Makefile.template
@@ -195,6 +195,10 @@
DEFINES += $(DEFINES_$(CONFIG)) INSTALL_PREFIX=\"$(prefix)\"
LDFLAGS += $(LDFLAGS_$(CONFIG))
+ifdef EXTRA_DEFINES
+DEFINES += EXTRA_DEFINES
+endif
+
CFLAGS += -std=c89 -pedantic
ifeq ($(HAS_CXX11),true)
CXXFLAGS += -std=c++11
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index fddd8eb..4e0ff85 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -201,7 +201,7 @@
languages = set(_LANGUAGES[l] for l in args.language)
build_steps = [jobset.JobSpec(['make',
'-j', '%d' % (multiprocessing.cpu_count() + 1),
- 'DEFINES=GRPC_TEST_SLOWDOWN_MACHINE_FACTOR=%f' % args.slowdown,
+ 'EXTRA_DEFINES=GRPC_TEST_SLOWDOWN_MACHINE_FACTOR=%f' % args.slowdown,
'CONFIG=%s' % cfg] + list(set(
itertools.chain.from_iterable(
l.make_targets() for l in languages))))