diff --git a/firmware/firmware.make b/firmware/firmware.make
index 8f8014d82c..3d79837871 100644
--- a/firmware/firmware.make
+++ b/firmware/firmware.make
@@ -46,7 +46,10 @@ $(BUILDDIR)/sysfont.o: $(SYSFONT) $(BUILDDIR)/sysfont.h
 	$(call PRINTS,CONVBDF $(subst $(ROOTDIR)/,,$<))$(TOOLSDIR)/convbdf -l $(MAXCHAR) -c -o $(BUILDDIR)/sysfont.c $<
 	$(call PRINTS,CC $(subst $(ROOTDIR)/,,$(BUILDDIR)/sysfont.c))$(CC) $(CFLAGS) -c $(BUILDDIR)/sysfont.c -o $@
 
-SVNVERSION:=$(shell $(TOOLSDIR)/version.sh $(ROOTDIR))
+# GNU make (at least) has a bug/feature that exported variable are not available
+# in the shell function (but are in recipe). Thus we need to explicitely pass
+# the VERSION environement variable
+SVNVERSION:=$(shell VERSION='$(VERSION)' $(TOOLSDIR)/version.sh $(ROOTDIR))
 OLDSVNVERSION:=$(shell grep 'RBVERSION' $(BUILDDIR)/rbversion.h 2>/dev/null|cut -d '"' -f 2 || echo "NOREVISION")
 
 ifneq ($(SVNVERSION),$(OLDSVNVERSION))
@@ -54,4 +57,4 @@ ifneq ($(SVNVERSION),$(OLDSVNVERSION))
 endif
 
 $(BUILDDIR)/rbversion.h:
-	$(call PRINTS,GEN $(@F))$(TOOLSDIR)/genversion.sh $(BUILDDIR) $(TOOLSDIR)/version.sh $(ROOTDIR)
+	$(call PRINTS,GEN $(@F))$(TOOLSDIR)/genversion.sh $(BUILDDIR) $(SVNVERSION)
diff --git a/tools/genversion.sh b/tools/genversion.sh
index bd80ceb597..c385c36924 100755
--- a/tools/genversion.sh
+++ b/tools/genversion.sh
@@ -6,19 +6,20 @@
 #   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 #                     \/            \/     \/    \/            \/
 
-# Usage: genversion.sh destination-dir path-to-version.sh [source-root]
+# Usage: genversion.sh destination-dir version
 
 # Generate rbversion.h file
 
 # XXX DO NOT TWEAK VERSION HERE, EDIT version.sh INSTEAD
 
-VERSION=`$2 $3`
+VERSION="$2"
 
 cat > "$1/_rbversion.h" << EOF
 /* Generated by genversion.sh */
 #define RBVERSION "$VERSION"
 EOF
 
+# Don't touch rbversion.h if it hasn't change, to avoid rebuilding stuff
 if [ -f "$1/rbversion.h" ]
     then if diff "$1/_rbversion.h" "$1/rbversion.h" > /dev/null
         then rm -f "$1/_rbversion.h"