diff --git a/sigal/__init__.py b/sigal/__init__.py
index ad148e8..a7172a4 100644
--- a/sigal/__init__.py
+++ b/sigal/__init__.py
@@ -117,8 +117,17 @@ def build(source, destination, debug, verbose, force, config, theme, title,
         logger.error("Input directory not found: %s", settings['source'])
         sys.exit(1)
 
-    if not os.path.relpath(settings['destination'],
-                           settings['source']).startswith('..'):
+    # on windows os.path.relpath raises a ValueError if the two paths are on 
+    # different drives, in that case we just ignore the exception as the two 
+    # paths are anyway not relative
+    relative_check = True
+    try:
+        relative_check =  os.path.relpath(settings['destination'],
+                           settings['source']).startswith('..')
+    except ValueError:
+        pass
+
+    if not relative_check:
         logger.error("Output directory should be outside of the input "
                      "directory.")
         sys.exit(1)