diff --git a/slave.mk b/slave.mk
index a650c3e6c2..b2d2c3bbf4 100644
--- a/slave.mk
+++ b/slave.mk
@@ -11,7 +11,7 @@ UID = $(shell id -u)
 GUID = $(shell id -g)
 
 ifeq ($(SONIC_IMAGE_VERSION),)
-	override SONIC_IMAGE_VERSION = $(shell export BUILD_TIMESTAMP=$(BUILD_TIMESTAMP) && export BUILD_NUMBER=$(BUILD_NUMBER) && . functions.sh && sonic_get_version)
+	override SONIC_IMAGE_VERSION := $(shell export BUILD_TIMESTAMP=$(BUILD_TIMESTAMP) && export BUILD_NUMBER=$(BUILD_NUMBER) && . functions.sh && sonic_get_version)
 endif
 
 .SECONDEXPANSION: