diff --git a/Makefile b/Makefile
index 957b7887530fa344436b325c9ab47b7cab85796a..f36e5af74962f7ea163b1c5d505f5f100e495257 100644
--- a/Makefile
+++ b/Makefile
@@ -22,7 +22,7 @@ s ?= ${ASDF_TEST_SYSTEMS}
 endif
 
 ifdef ASDF_DEVEL_SOURCE_REGISTRY
-CL_SOURCE_REGISTRY = ${ASDF_DEVEL_SOURCE_REGISTRY}
+export CL_SOURCE_REGISTRY = ${ASDF_DEVEL_SOURCE_REGISTRY}
 endif
 
 l ?= sbcl