diff --git a/mk/environ.mk b/mk/environ.mk
index d508562dfb..d7ca305eb6 100644
--- a/mk/environ.mk
+++ b/mk/environ.mk
@@ -53,6 +53,11 @@ ifneq ($(findstring CYGWIN, $(SYSTYPE)),)
     SKETCHBOOK	:= $(shell cygpath ${SKETCHBOOK})
 endif
 
+ifneq ($(wildcard $(SKETCHBOOK)/config.mk),)
+$(warning Reading $(SKETCHBOOK)/config.mk)
+include $(SKETCHBOOK)/config.mk
+endif
+
 #
 # Work out the sketch name from the name of the source directory.
 #
diff --git a/mk/px4_targets.mk b/mk/px4_targets.mk
index 99e127bd1b..7d3362ed78 100644
--- a/mk/px4_targets.mk
+++ b/mk/px4_targets.mk
@@ -1,6 +1,8 @@
 # PX4 build is via external build system
 
+ifeq ($(PX4_ROOT),)
 PX4_ROOT=../PX4Firmware
+endif
 
 # cope with relative paths
 ifeq ($(wildcard $(PX4_ROOT)/nuttx-configs),)