diff --git a/exec/Makefile b/exec/Makefile
index 8a4a1d48..5c6bc9c4 100644
--- a/exec/Makefile
+++ b/exec/Makefile
@@ -32,7 +32,7 @@
 
 # Include configuration
 #
-srcdir:=$(CURDIR)/../
+srcdir ?= $(CURDIR)/../
 
 include $(srcdir)Makefile.inc