diff --git a/loopy/kernel/__init__.py b/loopy/kernel/__init__.py
index ed01a32942c436cf81ef61881b5e124d37dc38b9..37aefec10bf61dc726b649b8d728aaccbb468932 100644
--- a/loopy/kernel/__init__.py
+++ b/loopy/kernel/__init__.py
@@ -786,6 +786,8 @@ class LoopKernel(ImmutableRecordWithoutPickling):
             for var_name in insn.read_dependency_names() & admissible_vars:
                 result.setdefault(var_name, set()).add(insn.id)
 
+        return result
+
     @memoize_method
     def writer_map(self):
         """