-MAKE_PARALLEL_JOBS = -j $(if $(shell [ -f /proc/cpuinfo ] && head /proc/cpuinfo), \
- $(shell expr 2 '*' $$(grep -c ^processor /proc/cpuinfo)), 2)
-MAKE_PARALLEL_FLAGS = $(if $($(PACKAGE)_make_parallel_fails),,$(MAKE_PARALLEL_JOBS))
+ifndef MAKE_PARALLEL_JOBS
+MAKE_PARALLEL_JOBS = $(if $(shell [ -f /proc/cpuinfo ] && head /proc/cpuinfo), \
+ $(shell grep -c ^processor /proc/cpuinfo), 2)
+endif
+MAKE_PARALLEL_FLAGS ?= $(if $($(PACKAGE)_make_parallel_fails),,-j $(MAKE_PARALLEL_JOBS))