diff --git a/pw_sync_embos/interrupt_spin_lock.cc b/pw_sync_embos/interrupt_spin_lock.cc
new file mode 100644
index 0000000..9d17ba6
--- /dev/null
+++ b/pw_sync_embos/interrupt_spin_lock.cc
@@ -0,0 +1,45 @@
+// Copyright 2021 The Pigweed Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#include "pw_sync/interrupt_spin_lock.h"
+
+#include "RTOS.h"
+#include "pw_assert/assert.h"
+
+namespace pw::sync {
+
+void InterruptSpinLock::lock() {
+  OS_IncDI();
+  // We can't deadlock here so crash instead.
+  PW_CHECK(!native_type_.locked.load(std::memory_order_relaxed),
+           "Recursive InterruptSpinLock::lock() detected");
+  native_type_.locked.store(true, std::memory_order_relaxed);
+}
+
+bool InterruptSpinLock::try_lock() {
+  OS_IncDI();
+  if (native_type_.locked.load(std::memory_order_relaxed)) {
+    OS_DecRI();  // Already locked, restore interrupts and bail out.
+    return false;
+  }
+  native_type_.locked.store(true, std::memory_order_relaxed);
+  return true;
+}
+
+void InterruptSpinLock::unlock() {
+  native_type_.locked.store(false, std::memory_order_relaxed);
+  OS_DecRI();
+}
+
+}  // namespace pw::sync