diff --git a/rules.mk b/rules.mk
index 16d6020e1a..dbc448e1a4 100644
--- a/rules.mk
+++ b/rules.mk
@@ -96,7 +96,7 @@ TARGET_SUFFIX=$(call qstrip,$(CONFIG_TARGET_SUFFIX))
 BUILD_SUFFIX:=$(call qstrip,$(CONFIG_BUILD_SUFFIX))
 SUBDIR:=$(patsubst $(TOPDIR)/%,%,${CURDIR})
 BUILD_SUBDIR:=$(patsubst $(TOPDIR)/%,%,${CURDIR})
-NPROC:=$(shell sysctl -n hw.ncpu 2>/dev/null || nproc)
+NPROC=$(shell sysctl -n hw.ncpu 2>/dev/null || nproc)
 export SHELL:=/usr/bin/env bash
 
 IS_PACKAGE_BUILD := $(if $(filter package/%,$(BUILD_SUBDIR)),1)