diff --git a/tools/Makefile.unix b/tools/Makefile.unix
index 122fa93ecbc..fac35b612e2 100644
--- a/tools/Makefile.unix
+++ b/tools/Makefile.unix
@@ -547,7 +547,7 @@ savedefconfig: do_savedefconfig
 	$(Q) grep "^CONFIG_ARCH_CHIP_" .config >> defconfig.tmp; true
 	$(Q) grep "CONFIG_ARCH_BOARD=" .config && grep "CONFIG_ARCH_BOARD=" .config >> defconfig.tmp; true
 	$(Q) grep "^CONFIG_ARCH_CUSTOM" .config && grep "^CONFIG_ARCH_CUSTOM" .config >> defconfig.tmp; true
-	$(Q) grep "^CONFIG_ARCH_BOARD_CUSTOM" .config && grep "^CONFIG_ARCH_BOARD_CUSTOM" .config >> defconfig.tmp; true
+	$(Q) grep "^CONFIG_ARCH_BOARD_CUSTOM=" .config && grep "^CONFIG_ARCH_BOARD_CUSTOM" .config >> defconfig.tmp; true
 	$(Q) export LC_ALL=C; cat defconfig.tmp | sort | uniq > sortedconfig.tmp
 	$(Q) echo "#" > warning.tmp
 	$(Q) echo "# This file is autogenerated: PLEASE DO NOT EDIT IT." >> warning.tmp
diff --git a/tools/Makefile.win b/tools/Makefile.win
index 1c5d12ddacd..b91a0773bfd 100644
--- a/tools/Makefile.win
+++ b/tools/Makefile.win
@@ -534,7 +534,7 @@ savedefconfig: do_savedefconfig
 	-$(Q) grep "^CONFIG_ARCH_CHIP_" .config >> defconfig.tmp
 	-$(Q) grep "CONFIG_ARCH_BOARD=" .config >> defconfig.tmp
 	-$(Q) grep "^CONFIG_ARCH_CUSTOM" .config >> defconfig.tmp
-	-$(Q) grep "^CONFIG_ARCH_BOARD_CUSTOM" .config >> defconfig.tmp
+	-$(Q) grep "^CONFIG_ARCH_BOARD_CUSTOM=" .config >> defconfig.tmp
 	$(Q) cat defconfig.tmp | sort | uniq > sortedconfig.tmp
 	$(Q) echo "#" > warning.tmp
 	$(Q) echo "# This file is autogenerated: PLEASE DO NOT EDIT IT." >> warning.tmp