diff --git a/third_party/blink/renderer/core/script_tools/model_context.cc b/third_party/blink/renderer/core/script_tools/model_context.cc
index 0fe934da99569..25cbb58fbb658 100644
--- a/third_party/blink/renderer/core/script_tools/model_context.cc
+++ b/third_party/blink/renderer/core/script_tools/model_context.cc
@@ -695,20 +695,22 @@ void ModelContext::RegisterDeclarativeTool(
 void ModelContext::OnToolExecuted(
     const base::UnguessableToken& invocation_id,
     base::expected<String, std::pair<ScriptValue, ScriptState*>> result) {
-  auto it = pending_executions_.find(String(invocation_id.ToString()));
-  if (it == pending_executions_.end()) {
+  // Remove the entry up front because the probes and the completion callback
+  // below may re-enter this object and mutate `pending_executions_`.
+  PendingExecution pending_execution =
+      pending_executions_.Take(String(invocation_id.ToString()));
+  if (!pending_execution.callback) {
     return;
   }
 
   if (result.has_value()) {
     probe::WebMCPToolResponded(document_, result.value(), invocation_id);
-    std::move(it->value.callback).Run(result.value());
+    std::move(pending_execution.callback).Run(result.value());
   } else {
     ScriptToolError error(ScriptToolErrorCode::kToolInvocationFailed);
     probe::WebMCPToolFailed(document_, error, invocation_id, result.error());
-    std::move(it->value.callback).Run(base::unexpected(error));
+    std::move(pending_execution.callback).Run(base::unexpected(error));
   }
-  pending_executions_.erase(it);
 }
 
 void ModelContext::MaybeRecordToolCount() {
diff --git a/third_party/blink/renderer/core/script_tools/model_context_test.cc b/third_party/blink/renderer/core/script_tools/model_context_test.cc
index ca2a149ce735b..df417eab006f7 100644
--- a/third_party/blink/renderer/core/script_tools/model_context_test.cc
+++ b/third_party/blink/renderer/core/script_tools/model_context_test.cc
@@ -1376,6 +1376,59 @@ TEST_F(ModelContextTest, CancelToolReentrancy) {
   run_loop.Run();
 }
 
+TEST_F(ModelContextTest, OnToolExecutedReentrancy) {
+  SimRequest main_resource("https://example.com/", "text/html");
+  LoadURL("https://example.com/");
+
+  main_resource.Complete(R"(
+    <body>
+    <script>
+    navigator.modelContext.registerTool({
+      execute: () => new Promise(() => {}),
+      name: "hang",
+      description: "never resolves",
+    });
+    navigator.modelContext.registerTool({
+      execute: async () => "done",
+      name: "echo",
+      description: "echo",
+    });
+    </script>
+  )");
+
+  auto* model_context = ModelContextSupplement::modelContext(GetDocument());
+  ASSERT_TRUE(model_context);
+
+  // Start enough long-running invocations that cancelling them all will cause
+  // the pending executions map to shrink its backing store.
+  Vector<base::UnguessableToken> hang_ids;
+  for (int i = 0; i < 32; ++i) {
+    base::UnguessableToken id = base::UnguessableToken::Create();
+    hang_ids.push_back(id);
+    model_context->ExecuteTool(id, "hang", "{}", /* signal= */ nullptr,
+                               base::DoNothing());
+  }
+
+  base::RunLoop run_loop;
+  String result;
+  model_context->ExecuteTool(
+      base::UnguessableToken::Create(), "echo", "{}", /* signal= */ nullptr,
+      base::BindLambdaForTesting(
+          [&](base::expected<String, ScriptToolError> res) {
+            // Cancel all other pending invocations from inside the completion
+            // callback.
+            for (const auto& id : hang_ids) {
+              model_context->CancelTool(id);
+            }
+            ASSERT_TRUE(res.has_value());
+            result = *res;
+            run_loop.Quit();
+          }));
+
+  run_loop.Run();
+  EXPECT_EQ(result, "done");
+}
+
 class MockDeclarativeTool : public GarbageCollected<MockDeclarativeTool>,
                             public DeclarativeWebMCPTool {
  public: