diff --git a/loopy/symbolic.py b/loopy/symbolic.py
index 816b607512b938850f4195d2cf6f8b16133e0cb9..50a2659ae58e5c8bedd27e4da0799a004073e936 100644
--- a/loopy/symbolic.py
+++ b/loopy/symbolic.py
@@ -97,7 +97,7 @@ class FunctionToPrimitiveMapper(IdentityMapper):
                 if not isinstance(expr.parameters[1], Variable):
                     raise TypeError("second argument to cse() must be a symbol")
                 return CommonSubexpression(
-                        expr.parameters[0], expr.parameters[1].name)
+                        self.rec(expr.parameters[0]), expr.parameters[1].name)
             else:
                 raise TypeError("cse takes two arguments")