diff --git a/make/projects-dir.mk b/make/projects-dir.mk
index 670aebf4..e0efebfc 100644
--- a/make/projects-dir.mk
+++ b/make/projects-dir.mk
@@ -6,7 +6,7 @@
 #
 # Some of its targets download software from janware GmbH servers. For those,
 # you will need a janware.com user account. Ask admin@janware.com if you want
-# one.
+# one, then define the JANWARE_USER=<janware user name> environment variable.
 #
 # Current documentation on how this Makefile is meant to be used can be found
 # under https://janware.com/wiki/pub/en/sw/build/. Running "make doc-module"
@@ -59,8 +59,12 @@ endif
 
 BUILD_PROJECTS = $(filter-out $(EXCLUDE_FROM_BUILD),$(PROJECTS))
 
-ifeq ($(JANWARE_USER),)
+ifndef ($(JANWARE_USER),)
   export JANWARE_USER = $(shell id -un)
+  $(warning Assuming JANWARE_USER=$(JANWARE_USER), explicitly set environment variable to turn off this warning!)
+endif
+
+ifeq ($(JANWARE_USER),)
   UNAVAILABLE_TARGETS ?= pull.done update.done clone.done
 else
   UNAVAILABLE_TARGETS ?=