diff --git a/loopy/subst.py b/loopy/subst.py
index b5b2145edadb72b648860ad7c1231088d14c7627..db94bb652b6862f5f35d38d4f1fc0ce29c8b395d 100644
--- a/loopy/subst.py
+++ b/loopy/subst.py
@@ -43,10 +43,12 @@ class ExprDescriptor(Record):
     __slots__ = ["insn", "expr", "unif_var_dict"]
 
 
-def extract_subst(kernel, subst_name, template, parameters):
+def extract_subst(kernel, subst_name, template, parameters=()):
     """
     :arg subst_name: The name of the substitution rule to be created.
     :arg template: Unification template expression.
+    :arg parameters: An iterable of parameters used in
+        *template*, or a comma-separated string of the same.
 
     All targeted subexpressions must match ('unify with') *template*
     The template may contain '*' wildcards that will have to match exactly across all
@@ -57,6 +59,10 @@ def extract_subst(kernel, subst_name, template, parameters):
         from pymbolic import parse
         template = parse(template)
 
+    if isinstance(parameters, str):
+        parameters = tuple(
+                s.strip() for s in parameters.split())
+
     var_name_gen = kernel.get_var_name_generator()
 
     # {{{ replace any wildcards in template with new variables
diff --git a/test/test_loopy.py b/test/test_loopy.py
index 17e28af6a05ef94abb5ba061271d9f7f5d4ec617..564291316f2f3ef8c43ded75219327d5098afc61 100644
--- a/test/test_loopy.py
+++ b/test/test_loopy.py
@@ -84,6 +84,23 @@ def test_complicated_subst(ctx_factory):
         assert substs_with_letter == how_many
 
 
+def test_extract_subst(ctx_factory):
+    knl = lp.make_kernel(
+            "{[i]: 0<=i<n}",
+            """
+                a[i] = 23*b[i]**2 + 25*b[i]**2
+                """)
+
+    knl = lp.extract_subst(knl, "bsquare", "alpha*b[i]**2", "alpha")
+
+    print(knl)
+
+    from loopy.symbolic import parse
+
+    insn, = knl.instructions
+    assert insn.expression == parse("bsquare(23) + bsquare(25)")
+
+
 def test_type_inference_no_artificial_doubles(ctx_factory):
     ctx = ctx_factory()