diff --git a/src/vpp-api/python/vpp_papi/vpp_papi.py b/src/vpp-api/python/vpp_papi/vpp_papi.py
index e67ee19..a9edfed 100644
--- a/src/vpp-api/python/vpp_papi/vpp_papi.py
+++ b/src/vpp-api/python/vpp_papi/vpp_papi.py
@@ -154,7 +154,7 @@
 
 class VPPApiJSONFiles:
     @classmethod
-    def find_api_dir(cls, dirs):
+    def find_api_dir(cls, dirs=[]):
         """Attempt to find the best directory in which API definition
         files may reside. If the value VPP_API_DIR exists in the environment
         then it is first on the search list. If we're inside a recognized
@@ -170,6 +170,9 @@
         # in which case, plot a course to likely places in the src tree
         import __main__ as main
 
+        if os.getenv("VPP_API_DIR"):
+            dirs.append(os.getenv("VPP_API_DIR"))
+
         if hasattr(main, "__file__"):
             # get the path of the calling script
             localdir = os.path.dirname(os.path.realpath(main.__file__))