diff --git a/cubed/extensions/mem_warn.py b/cubed/extensions/mem_warn.py
new file mode 100644
index 00000000..03f5b2bf
--- /dev/null
+++ b/cubed/extensions/mem_warn.py
@@ -0,0 +1,35 @@
+import warnings
+from collections import Counter
+
+from cubed.runtime.pipeline import visit_nodes
+from cubed.runtime.types import Callback
+
+
+class MemoryWarningCallback(Callback):
+    def on_compute_start(self, event):
+        # store ops keyed by name
+        self.ops = {}
+        for name, node in visit_nodes(event.dag, event.resume):
+            primitive_op = node["primitive_op"]
+            self.ops[name] = primitive_op
+
+        # count number of times each op exceeds allowed mem
+        self.counter = Counter()
+
+    def on_task_end(self, event):
+        allowed_mem = self.ops[event.name].allowed_mem
+        if (
+            event.peak_measured_mem_end is not None
+            and event.peak_measured_mem_end > allowed_mem
+        ):
+            self.counter.update({event.name: 1})
+
+    def on_compute_end(self, event):
+        if sum(self.counter.values()) > 0:
+            exceeded = [
+                f"{k} ({v}/{self.ops[k].num_tasks})" for k, v in self.counter.items()
+            ]
+            warnings.warn(
+                f"Peak memory usage exceeded allowed_mem when running tasks: {', '.join(exceeded)}",
+                UserWarning,
+            )
diff --git a/cubed/tests/test_executor_features.py b/cubed/tests/test_executor_features.py
index 6ba3f2cc..22fce7bf 100644
--- a/cubed/tests/test_executor_features.py
+++ b/cubed/tests/test_executor_features.py
@@ -13,6 +13,7 @@
 import cubed.array_api as xp
 import cubed.random
 from cubed.extensions.history import HistoryCallback
+from cubed.extensions.mem_warn import MemoryWarningCallback
 from cubed.extensions.rich import RichProgressBar
 from cubed.extensions.timeline import TimelineVisualizationCallback
 from cubed.extensions.tqdm import TqdmProgressBar
@@ -148,6 +149,28 @@ def test_callbacks_modal(spec, modal_executor):
         fs.rm(tmp_path, recursive=True)
 
 
+@pytest.mark.skipif(
+    platform.system() == "Windows", reason="measuring memory does not run on windows"
+)
+def test_mem_warn(tmp_path, executor):
+    if executor.name not in ("processes", "lithops"):
+        pytest.skip(f"{executor.name} executor does not support MemoryWarningCallback")
+
+    spec = cubed.Spec(tmp_path, allowed_mem=200_000_000, reserved_mem=100_000_000)
+    mem_warn = MemoryWarningCallback()
+
+    def func(a):
+        np.ones(100_000_000)  # blow memory
+        return a
+
+    a = xp.asarray([[1, 2, 3], [4, 5, 6], [7, 8, 9]], chunks=(2, 2), spec=spec)
+    b = cubed.map_blocks(func, a, dtype=a.dtype)
+    with pytest.raises(
+        UserWarning, match="Peak memory usage exceeded allowed_mem when running tasks"
+    ):
+        b.compute(executor=executor, callbacks=[mem_warn])
+
+
 def test_resume(spec, executor):
     if executor.name == "beam":
         pytest.skip(f"{executor.name} executor does not support resume")
diff --git a/cubed/tests/test_mem_utilization.py b/cubed/tests/test_mem_utilization.py
index 853f993f..85f067c8 100644
--- a/cubed/tests/test_mem_utilization.py
+++ b/cubed/tests/test_mem_utilization.py
@@ -14,6 +14,7 @@
 import cubed.random
 from cubed.backend_array_api import namespace as nxp
 from cubed.extensions.history import HistoryCallback
+from cubed.extensions.mem_warn import MemoryWarningCallback
 from cubed.runtime.executors.lithops import LithopsExecutor
 from cubed.tests.utils import LITHOPS_LOCAL_CONFIG
 
@@ -277,12 +278,13 @@ def run_operation(tmp_path, name, result_array, *, optimize_function=None):
     # result_array.visualize(f"cubed-{name}", optimize_function=optimize_function)
     executor = LithopsExecutor(config=LITHOPS_LOCAL_CONFIG)
     hist = HistoryCallback()
+    mem_warn = MemoryWarningCallback()
     # use store=None to write to temporary zarr
     cubed.to_zarr(
         result_array,
         store=None,
         executor=executor,
-        callbacks=[hist],
+        callbacks=[hist, mem_warn],
         optimize_function=optimize_function,
     )