diff --git a/tools/building.py b/tools/building.py
index 726056533f88f4a8f8f50a10745437620ed7747b..3572daabbe38e16460cb761bb8b09d47c8521c3f 100644
--- a/tools/building.py
+++ b/tools/building.py
@@ -43,8 +43,9 @@ class Win32Spawn:
             proc = subprocess.Popen(cmdline, env=_e,
                     startupinfo=startupinfo, shell=False)
         except Exception as e:
-            print 'Error in Popen: %s' % e
-            return -1
+            print 'Error in calling:\n%s' % cmdline
+            print 'Exception: %s: %s' % (e, os.strerror(e.errno))
+            return e.errno
         finally:
             os.environ['PATH'] = old_path