diff --git a/boxtree/tree_build_kernels.py b/boxtree/tree_build_kernels.py
index 1dd74cb1b9ab9eebc24be2b0d2087067890f0fdc..c8b5fa51b52979f76f5cb66fe05464293ed0b4d6 100644
--- a/boxtree/tree_build_kernels.py
+++ b/boxtree/tree_build_kernels.py
@@ -122,7 +122,7 @@ class _KernelInfo(Record):
 refine_weight_dtype = np.dtype(np.int32)
 
 
-@memoize
+@memoize(use_kwargs=True)
 def make_morton_bin_count_type(device, dimensions, particle_id_dtype,
         srcntgts_have_extent):
     fields = []
diff --git a/requirements.txt b/requirements.txt
index 80b397a0d4a76b96a1069249290dbf8f44a30e56..5bb27fd514bc982541819de777204e92752880c7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,6 @@
+# https://github.com/illinois-ceesd/mirgecom/issues/302
+decorator<5
+
 numpy
 git+https://github.com/inducer/pyopencl#egg=pyopencl
 git+https://github.com/inducer/pymbolic#egg=pymbolic