diff --git a/pyproject.toml b/pyproject.toml
index 93f709e..7d127f6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "pfun"
-version = "0.12.1"
+version = "0.12.2"
 description = ""
 authors = ["Sune Debel <sad@archii.ai>"]
 readme = "README.md"
diff --git a/src/pfun/effect.pyx b/src/pfun/effect.pyx
index 9de1f34..185628e 100644
--- a/src/pfun/effect.pyx
+++ b/src/pfun/effect.pyx
@@ -27,18 +27,25 @@ cdef class RuntimeEnv:
     """
     cdef object r
     cdef object exit_stack
-    cdef object process_executor
-    cdef object thread_executor
+    cdef object max_processes
+    cdef object max_threads
+    cdef readonly object process_executor
+    cdef readonly object thread_executor
 
-    def __cinit__(self, r, exit_stack, process_executor, thread_executor):
+    def __cinit__(self, r, exit_stack, max_processes, max_threads):
         self.r = r
         self.exit_stack = exit_stack
-        self.process_executor = process_executor
-        self.thread_executor = thread_executor
+        self.max_processes = max_processes
+        self.max_threads = max_threads
+        self.process_executor = None
+        self.thread_executor = None
     
     async def run_in_process_executor(self, f, *args, **kwargs):
         loop = asyncio.get_running_loop()
         payload = dill.dumps((f, args, kwargs))
+        if self.process_executor is None:
+            self.process_executor = ProcessPoolExecutor(max_workers=self.max_processes)
+            self.exit_stack.enter_context(self.process_executor)
         return dill.loads(
             await loop.run_in_executor(
                 self.process_executor, run_dill_encoded, payload
@@ -47,6 +54,9 @@ cdef class RuntimeEnv:
 
     async def run_in_thread_executor(self, f, *args, **kwargs):
         loop = asyncio.get_running_loop()
+        if self.thread_executor is None:
+            self.thread_executor = ThreadPoolExecutor(max_workers=self.max_threads)
+            self.exit_stack.enter_context(self.thread_executor)
         return await loop.run_in_executor(
             self.thread_executor, lambda: f(*args, **kwargs)
         )
@@ -100,12 +110,8 @@ cdef class CEffect:
                           Exception
         """
         stack = AsyncExitStack()
-        process_executor = ProcessPoolExecutor(max_workers=max_processes)
-        thread_executor = ThreadPoolExecutor(max_workers=max_threads)
         async with stack:
-            stack.enter_context(process_executor)
-            stack.enter_context(thread_executor)
-            env = RuntimeEnv(r, stack, process_executor, thread_executor)
+            env = RuntimeEnv(r, stack, max_processes, max_threads)
             effect = await self.do(env)
             if isinstance(effect, CSuccess):
                 return effect.result
diff --git a/tests/test_effect.py b/tests/test_effect.py
index e1413e8..2544d0f 100644
--- a/tests/test_effect.py
+++ b/tests/test_effect.py
@@ -1,3 +1,4 @@
+from contextlib import ExitStack
 from subprocess import CalledProcessError
 from unittest import mock
 
@@ -236,6 +237,15 @@ def test_catch_cpu_bound(self, f):
     def test_catch_io_bound(self, f):
         assert effect.catch_io_bound(Exception)(f)(None).run(None) == f(None)
 
+    @pytest.mark.asyncio
+    @given(anything())
+    async def test_process_and_thread_pool_initialized_lazily(self, value):
+        with ExitStack() as stack:
+            env = effect.RuntimeEnv(None, stack, 1, 1)
+            await effect.success(value).do(env)
+            assert env.process_executor is None
+            assert env.thread_executor is None
+
     def test_success_repr(self):
         assert repr(effect.success('value')) == 'success(\'value\')'