diff --git a/lib/Makefile b/lib/Makefile
index fc9d6a6ce..bc45f9b0d 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -226,7 +226,7 @@ ifeq ($(BUILD_DIR),0)
 .PHONY: libzstd.a  # not the actual recipe
 libzstd.a:
 	$(MAKE) --no-print-directory $@ \
-        BUILD_DIR=obj/conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) | $(HASH) | head -c 16) \
+        BUILD_DIR=obj/conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | head -c 16) \
         CPPFLAGS="$(CPPFLAGS)"
 
 else
@@ -266,7 +266,7 @@ ifeq ($(BUILD_DIR),0)
 .PHONY: $(LIBZSTD)  # not the actual recipe
 $(LIBZSTD):
 	$(MAKE) --no-print-directory $@ \
-        BUILD_DIR=obj/conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) | $(HASH) | head -c 16) \
+        BUILD_DIR=obj/conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | head -c 16) \
         CPPFLAGS="$(CPPFLAGS)" \
         CFLAGS="$(CFLAGS)" \
         LDFLAGS="$(LDFLAGS)"
diff --git a/tests/libzstd_partial_builds.sh b/tests/libzstd_partial_builds.sh
index b1c1e3b1a..bee2dbda5 100755
--- a/tests/libzstd_partial_builds.sh
+++ b/tests/libzstd_partial_builds.sh
@@ -22,7 +22,6 @@ mustBeAbsent() {
 }
 
 # default compilation : all features enabled
-make clean > /dev/null
 $ECHO "testing default library compilation"
 CFLAGS= make -C $DIR/../lib libzstd.a > $INTOVOID
 nm $DIR/../lib/libzstd.a | $GREP "\.o" > tmplog