diff --git a/loopy/codegen/__init__.py b/loopy/codegen/__init__.py
index 07bcdc7c6c4a0c23d374a14bc21e4e161b73be03..79adb922d69c6eb81212fd061e667b6529bc6852 100644
--- a/loopy/codegen/__init__.py
+++ b/loopy/codegen/__init__.py
@@ -28,7 +28,7 @@ from loopy.diagnostic import LoopyError, warn
 from pytools import ImmutableRecord
 import islpy as isl
 
-from pytools.persistent_dict import PersistentDict
+from pytools.persistent_dict import WriteOncePersistentDict
 from loopy.tools import LoopyKeyBuilder
 from loopy.version import DATA_MODEL_VERSION
 
@@ -357,8 +357,9 @@ class CodeGenerationState(object):
 # }}}
 
 
-code_gen_cache = PersistentDict("loopy-code-gen-cache-v3-"+DATA_MODEL_VERSION,
-        key_builder=LoopyKeyBuilder())
+code_gen_cache = WriteOncePersistentDict(
+         "loopy-code-gen-cache-v3-"+DATA_MODEL_VERSION,
+         key_builder=LoopyKeyBuilder())
 
 
 class PreambleInfo(ImmutableRecord):
@@ -515,7 +516,7 @@ def generate_code_v2(kernel):
     logger.info("%s: generate code: done" % kernel.name)
 
     if CACHING_ENABLED:
-        code_gen_cache[input_kernel] = codegen_result
+        code_gen_cache.store_if_not_present(input_kernel, codegen_result)
 
     return codegen_result
 
diff --git a/loopy/execution.py b/loopy/execution.py
index 07e28f06d33e5884ac57c9505593c9ee916c3171..a1228f8f3bb3493e83936ee0b3998bbd5b8cdcc2 100644
--- a/loopy/execution.py
+++ b/loopy/execution.py
@@ -31,7 +31,7 @@ from loopy.diagnostic import LoopyError
 import logging
 logger = logging.getLogger(__name__)
 
-from pytools.persistent_dict import PersistentDict
+from pytools.persistent_dict import WriteOncePersistentDict
 from loopy.tools import LoopyKeyBuilder
 from loopy.version import DATA_MODEL_VERSION
 
@@ -120,7 +120,7 @@ class SeparateArrayPackingController(object):
 
 # {{{ KernelExecutorBase
 
-typed_and_scheduled_cache = PersistentDict(
+typed_and_scheduled_cache = WriteOncePersistentDict(
         "loopy-typed-and-scheduled-cache-v1-"+DATA_MODEL_VERSION,
         key_builder=LoopyKeyBuilder())
 
@@ -204,7 +204,7 @@ class KernelExecutorBase(object):
         kernel = self.get_typed_and_scheduled_kernel_uncached(arg_to_dtype_set)
 
         if CACHING_ENABLED:
-            typed_and_scheduled_cache[cache_key] = kernel
+            typed_and_scheduled_cache.store_if_not_present(cache_key, kernel)
 
         return kernel
 
diff --git a/loopy/preprocess.py b/loopy/preprocess.py
index 541b44f58c5b02e9beba15211cb861fd09f14096..29d8888ae3b0e488ab82beb4b654106988bcf803 100644
--- a/loopy/preprocess.py
+++ b/loopy/preprocess.py
@@ -30,7 +30,7 @@ from loopy.diagnostic import (
 
 import islpy as isl
 
-from pytools.persistent_dict import PersistentDict
+from pytools.persistent_dict import WriteOncePersistentDict
 
 from loopy.tools import LoopyKeyBuilder
 from loopy.version import DATA_MODEL_VERSION
@@ -2020,7 +2020,8 @@ def limit_boostability(kernel):
 # }}}
 
 
-preprocess_cache = PersistentDict("loopy-preprocess-cache-v2-"+DATA_MODEL_VERSION,
+preprocess_cache = WriteOncePersistentDict(
+        "loopy-preprocess-cache-v2-"+DATA_MODEL_VERSION,
         key_builder=LoopyKeyBuilder())
 
 
@@ -2126,7 +2127,7 @@ def preprocess_kernel(kernel, device=None):
     # }}}
 
     if CACHING_ENABLED:
-        preprocess_cache[input_kernel] = kernel
+        preprocess_cache.store_if_not_present(input_kernel, kernel)
 
     return kernel
 
diff --git a/loopy/schedule/__init__.py b/loopy/schedule/__init__.py
index d28e7b1b3def2b988b4624aed9caf8f65c70b2c5..3d47a5ec5ff33f7d8184acd8fde92aeaf1855378 100644
--- a/loopy/schedule/__init__.py
+++ b/loopy/schedule/__init__.py
@@ -29,7 +29,7 @@ import sys
 import islpy as isl
 from loopy.diagnostic import warn_with_kernel, LoopyError  # noqa
 
-from pytools.persistent_dict import PersistentDict
+from pytools.persistent_dict import WriteOncePersistentDict
 from loopy.tools import LoopyKeyBuilder
 from loopy.version import DATA_MODEL_VERSION
 
@@ -1940,7 +1940,8 @@ def generate_loop_schedules_inner(kernel, debug_args={}):
 # }}}
 
 
-schedule_cache = PersistentDict("loopy-schedule-cache-v4-"+DATA_MODEL_VERSION,
+schedule_cache = WriteOncePersistentDict(
+        "loopy-schedule-cache-v4-"+DATA_MODEL_VERSION,
         key_builder=LoopyKeyBuilder())
 
 
@@ -1971,7 +1972,7 @@ def get_one_scheduled_kernel(kernel):
             kernel.name, time()-start_time))
 
     if CACHING_ENABLED and not from_cache:
-        schedule_cache[sched_cache_key] = result
+        schedule_cache.store_if_not_present(sched_cache_key, result)
 
     return result
 
diff --git a/loopy/transform/buffer.py b/loopy/transform/buffer.py
index 92cff7a507d672a3acc51a8abed572a04cb7e86a..1b059b6a73d3064596b8679fbc87f94287b2d9fe 100644
--- a/loopy/transform/buffer.py
+++ b/loopy/transform/buffer.py
@@ -29,7 +29,7 @@ from loopy.symbolic import (get_dependencies,
         RuleAwareIdentityMapper, SubstitutionRuleMappingContext,
         SubstitutionMapper)
 from pymbolic.mapper.substitutor import make_subst_func
-from pytools.persistent_dict import PersistentDict
+from pytools.persistent_dict import WriteOncePersistentDict
 from loopy.tools import LoopyKeyBuilder, PymbolicExpressionHashWrapper
 from loopy.version import DATA_MODEL_VERSION
 from loopy.diagnostic import LoopyError
@@ -124,7 +124,8 @@ class ArrayAccessReplacer(RuleAwareIdentityMapper):
 # }}}
 
 
-buffer_array_cache = PersistentDict("loopy-buffer-array-cache-"+DATA_MODEL_VERSION,
+buffer_array_cache = WriteOncePersistentDict(
+        "loopy-buffer-array-cache-"+DATA_MODEL_VERSION,
         key_builder=LoopyKeyBuilder())
 
 
@@ -531,7 +532,8 @@ def buffer_array(kernel, var_name, buffer_inames, init_expression=None,
 
     if CACHING_ENABLED:
         from loopy.preprocess import prepare_for_caching
-        buffer_array_cache[cache_key] = prepare_for_caching(kernel)
+        buffer_array_cache.store_if_not_present(
+                cache_key, prepare_for_caching(kernel))
 
     return kernel
 
diff --git a/setup.py b/setup.py
index 67d943af3be4446834bf7262a91b8596b601ca85..94843bf69e4e25677ccc0713e5f598e9dcfd55e2 100644
--- a/setup.py
+++ b/setup.py
@@ -37,7 +37,7 @@ setup(name="loo.py",
           ],
 
       install_requires=[
-          "pytools>=2017.3",
+          "pytools>=2017.6",
           "pymbolic>=2016.2",
           "genpy>=2016.1.2",
           "cgen>=2016.1",