diff --git a/embassy-sync/src/lazy_lock.rs b/embassy-sync/src/lazy_lock.rs
index 18e3c2019..f1bd88b61 100644
--- a/embassy-sync/src/lazy_lock.rs
+++ b/embassy-sync/src/lazy_lock.rs
@@ -31,7 +31,12 @@ union Data<T, F> {
     f: ManuallyDrop<F>,
 }
 
-unsafe impl<T, F> Sync for LazyLock<T, F> {}
+unsafe impl<T, F> Sync for LazyLock<T, F>
+where
+    T: Sync,
+    F: Sync,
+{
+}
 
 impl<T, F: FnOnce() -> T> LazyLock<T, F> {
     /// Create a new uninitialized `StaticLock`.
diff --git a/embassy-sync/src/once_lock.rs b/embassy-sync/src/once_lock.rs
index cd05b986d..1e848685a 100644
--- a/embassy-sync/src/once_lock.rs
+++ b/embassy-sync/src/once_lock.rs
@@ -42,7 +42,7 @@ pub struct OnceLock<T> {
     data: Cell<MaybeUninit<T>>,
 }
 
-unsafe impl<T> Sync for OnceLock<T> {}
+unsafe impl<T> Sync for OnceLock<T> where T: Sync {}
 
 impl<T> OnceLock<T> {
     /// Create a new uninitialized `OnceLock`.