diff --git a/Tests/Functional/lit.cfg b/Tests/Functional/lit.cfg
index a8a8f05..2b58f02 100644
--- a/Tests/Functional/lit.cfg
+++ b/Tests/Functional/lit.cfg
@@ -37,8 +37,10 @@
     return value
 
 built_products_dir = _getenv('BUILT_PRODUCTS_DIR')
+# Force tests to build with -swift-version 3 for now.
 swift_exec = [
     _getenv('SWIFT_EXEC'),
+    '-swift-version', '3',
     '-Xlinker', '-rpath',
     '-Xlinker', built_products_dir,
     '-L', built_products_dir,