diff -r 74e3c7359393 SConstruct
--- a/SConstruct	Wed Apr 22 20:22:29 2015 -0700
+++ b/SConstruct	Thu Apr 30 14:34:02 2015 +0100
@@ -237,9 +237,10 @@
     Exit(1)
 
 # Check that swig is present
-if not 'SWIG' in main_dict_keys:
-    print "swig is not installed (package swig on Ubuntu and RedHat)"
-    Exit(1)
+if not ('SWIG' in main_dict_keys or \
+    'SWIG' in main.Dictionary()['ENV']):
+        print "swig is not installed (package swig on Ubuntu and RedHat)"
+        Exit(1)
 
 # add useful python code PYTHONPATH so it can be used by subprocesses
 # as well
@@ -399,7 +400,7 @@
 global_vars.AddVariables(
     ('CC', 'C compiler', environ.get('CC', main['CC'])),
     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
-    ('SWIG', 'SWIG tool', environ.get('SWIG', main['SWIG'])),
+    ('SWIG', 'SWIG tool', environ.get('SWIG', main.get('SWIG'))),
     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
     ('BATCH', 'Use batch pool for build and tests', False),
     ('BATCH_CMD', 'Batch pool submission command name', 'qdo'),