diff --git a/loopy/kernel/__init__.py b/loopy/kernel/__init__.py
index 24f0ebb1492f09c2dd97969b1b12581cc4168229..bdef1133e5e0a37d66e6d427dba91cc42213b3b1 100644
--- a/loopy/kernel/__init__.py
+++ b/loopy/kernel/__init__.py
@@ -959,7 +959,8 @@ 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