diff --git a/docker/Makefile b/docker/Makefile
index cd0930bd..cd37fb50 100644
--- a/docker/Makefile
+++ b/docker/Makefile
@@ -14,6 +14,9 @@
 # limitations under the License.
 # ------------------------------------------------------------------------------
 
+# PDO_SOURCE_ROOT
+PDO_SOURCE_ROOT ?= $(shell readlink -f ..)
+
 # PDO_REPO --
 #   The URL or path to the git repository, the default uses the current repository
 #   though it might be reasonable to build a particular branch from the primary