diff --git a/loopy/kernel/__init__.py b/loopy/kernel/__init__.py
index 642c82c4b02c5b07fb6275a18ed49a8b8ee39104..9e423b99f4f1aeeab5b54557a1ae7d14fca92d4a 100644
--- a/loopy/kernel/__init__.py
+++ b/loopy/kernel/__init__.py
@@ -958,7 +958,8 @@ class LoopKernel(ImmutableRecordWithoutPickling):
             try:
                 # insist block size is constant
                 size = static_max_of_pw_aff(size,
-                        constants_only=isinstance(tag, LocalIndexTag))
+                        constants_only=isinstance(tag, LocalIndexTag),
+                        context=self.assumptions)
             except ValueError:
                 pass