diff --git a/loopy/subst.py b/loopy/subst.py
index db94bb652b6862f5f35d38d4f1fc0ce29c8b395d..fa302d667310c13b09494db9127efa7f96273d73 100644
--- a/loopy/subst.py
+++ b/loopy/subst.py
@@ -61,7 +61,7 @@ def extract_subst(kernel, subst_name, template, parameters=()):
 
     if isinstance(parameters, str):
         parameters = tuple(
-                s.strip() for s in parameters.split())
+                s.strip() for s in parameters.split(","))
 
     var_name_gen = kernel.get_var_name_generator()