diff --git a/mk/environ.mk b/mk/environ.mk
index 18a9ca9767..bb4cbd6a59 100644
--- a/mk/environ.mk
+++ b/mk/environ.mk
@@ -4,7 +4,7 @@
 #
 SYSTYPE			:=	$(shell uname)
 
-GIT_VERSION := $(shell git rev-parse HEAD | cut -c1-8)
+GIT_VERSION ?= $(shell git rev-parse HEAD | cut -c1-8)
 EXTRAFLAGS += -DGIT_VERSION="\"$(GIT_VERSION)\""
 
 # Add missing parts from libc and libstdc++ for all boards
diff --git a/mk/px4_targets.mk b/mk/px4_targets.mk
index 112dc92ef6..fe6c270c1a 100644
--- a/mk/px4_targets.mk
+++ b/mk/px4_targets.mk
@@ -33,8 +33,8 @@ ifneq ($(wildcard $(SKETCHBOOK)/../uavcan),)
 $(warning *** You have an old uavcan tree - see http://dev.ardupilot.com/wiki/git-submodules/)
 endif
 
-NUTTX_GIT_VERSION := $(shell cd $(NUTTX_SRC) && git rev-parse HEAD | cut -c1-8)
-PX4_GIT_VERSION   := $(shell cd $(PX4_ROOT) && git rev-parse HEAD | cut -c1-8)
+NUTTX_GIT_VERSION ?= $(shell cd $(NUTTX_SRC) && git rev-parse HEAD | cut -c1-8)
+PX4_GIT_VERSION   ?= $(shell cd $(PX4_ROOT) && git rev-parse HEAD | cut -c1-8)
 
 EXTRAFLAGS += -DNUTTX_GIT_VERSION="\"$(NUTTX_GIT_VERSION)\""
 EXTRAFLAGS += -DPX4_GIT_VERSION="\"$(PX4_GIT_VERSION)\""