diff --git a/test/test_all.py b/test/test_all.py
index 25520f139..e94988041 100644
--- a/test/test_all.py
+++ b/test/test_all.py
@@ -1,4 +1,18 @@
 #!/usr/bin/python
+import os
+
+# clear environment for testing
+#
+for s in (
+    'BOOST_ROOT','BOOST_BUILD_PATH','JAM_TOOLSET','BCCROOT',
+    'MSVCDir','MSVC','MSVCNT','MINGW','watcom'
+    ):
+    
+    try:
+        del os.environ[s]
+    except:
+        pass
+
 import startup_v1
 import startup_v2
 import project_test1