diff --git a/embassy-extras/src/peripheral.rs b/embassy-extras/src/peripheral.rs
index edc5fe955..2358ab96f 100644
--- a/embassy-extras/src/peripheral.rs
+++ b/embassy-extras/src/peripheral.rs
@@ -5,18 +5,26 @@ use core::ptr;
 
 use embassy::interrupt::{Interrupt, InterruptExt};
 
+/// A version of `PeripheralState` without the `'static` bound,
+/// for cases where the compiler can't statically make sure
+/// that `on_interrupt` doesn't reference anything which might be invalidated.
+///
 /// # Safety
 /// When types implementing this trait are used with `PeripheralMutex`,
 /// no fields referenced by `on_interrupt`'s lifetimes must end without first calling `Drop` on the `PeripheralMutex`.
-pub unsafe trait PeripheralStateUnchecked {
+pub unsafe trait PeripheralStateUnchecked: Send {
     type Interrupt: Interrupt;
     fn on_interrupt(&mut self);
 }
 
-// `PeripheralMutex` is safe because `Pin` guarantees that the memory it references will not be invalidated or reused
-// without calling `Drop`. However, it provides no guarantees about references contained within the state still being valid,
-// so this `'static` bound is necessary.
-pub trait PeripheralState: 'static {
+/// A type which can be used as state with `PeripheralMutex`.
+///
+/// It needs to be `Send` because `&mut` references are sent back and forth between the 'thread' which owns the `PeripheralMutex` and the interrupt,
+/// and `&mut T` is `Send` where `T: Send`.
+///
+/// It also requires `'static`, because although `Pin` guarantees that the memory of the state won't be invalidated,
+/// it doesn't guarantee that the lifetime will last.
+pub trait PeripheralState: Send + 'static {
     type Interrupt: Interrupt;
     fn on_interrupt(&mut self);
 }
diff --git a/embassy-extras/src/peripheral_shared.rs b/embassy-extras/src/peripheral_shared.rs
index 820622bb9..5961441e0 100644
--- a/embassy-extras/src/peripheral_shared.rs
+++ b/embassy-extras/src/peripheral_shared.rs
@@ -4,18 +4,25 @@ use core::ptr;
 
 use embassy::interrupt::{Interrupt, InterruptExt};
 
+/// A version of `PeripheralState` without the `'static` bound,
+/// for cases where the compiler can't statically make sure
+/// that `on_interrupt` doesn't reference anything which might be invalidated.
+///
 /// # Safety
 /// When types implementing this trait are used with `Peripheral`,
 /// no fields referenced by `on_interrupt`'s lifetimes must end without first calling `Drop` on the `Peripheral`.
-pub unsafe trait PeripheralStateUnchecked {
+pub unsafe trait PeripheralStateUnchecked: Sync {
     type Interrupt: Interrupt;
     fn on_interrupt(&self);
 }
 
-// `Peripheral` is safe because `Pin` guarantees that the memory it references will not be invalidated or reused
-// without calling `Drop`. However, it provides no guarantees about references contained within the state still being valid,
-// so this `'static` bound is necessary.
-pub trait PeripheralState: 'static {
+/// A type which can be used as state with `Peripheral`.
+///
+/// It needs to be `Sync` because references are shared between the 'thread' which owns the `Peripheral` and the interrupt.
+///
+/// It also requires `'static`, because although `Pin` guarantees that the memory of the state won't be invalidated,
+/// it doesn't guarantee that the lifetime will last.
+pub trait PeripheralState: Sync + 'static {
     type Interrupt: Interrupt;
     fn on_interrupt(&self);
 }
diff --git a/embassy-extras/src/usb/mod.rs b/embassy-extras/src/usb/mod.rs
index 330eb9220..481987a6c 100644
--- a/embassy-extras/src/usb/mod.rs
+++ b/embassy-extras/src/usb/mod.rs
@@ -14,7 +14,7 @@ use embassy::interrupt::Interrupt;
 use usb_serial::{ReadInterface, UsbSerial, WriteInterface};
 
 /// Marker trait to mark an interrupt to be used with the [`Usb`] abstraction.
-pub unsafe trait USBInterrupt: Interrupt {}
+pub unsafe trait USBInterrupt: Interrupt + Send {}
 
 pub(crate) struct State<'bus, B, T, I>
 where
@@ -140,7 +140,7 @@ where
     }
 }
 
-pub trait ClassSet<B: UsbBus> {
+pub trait ClassSet<B: UsbBus>: Send {
     fn poll_all(&mut self, device: &mut UsbDevice<'_, B>) -> bool;
 }
 
@@ -176,8 +176,8 @@ pub struct Index1;
 
 impl<B, C1> ClassSet<B> for ClassSet1<B, C1>
 where
-    B: UsbBus,
-    C1: UsbClass<B>,
+    B: UsbBus + Send,
+    C1: UsbClass<B> + Send,
 {
     fn poll_all(&mut self, device: &mut UsbDevice<'_, B>) -> bool {
         device.poll(&mut [&mut self.class])
@@ -186,9 +186,9 @@ where
 
 impl<B, C1, C2> ClassSet<B> for ClassSet2<B, C1, C2>
 where
-    B: UsbBus,
-    C1: UsbClass<B>,
-    C2: UsbClass<B>,
+    B: UsbBus + Send,
+    C1: UsbClass<B> + Send,
+    C2: UsbClass<B> + Send,
 {
     fn poll_all(&mut self, device: &mut UsbDevice<'_, B>) -> bool {
         device.poll(&mut [&mut self.class1, &mut self.class2])
@@ -197,8 +197,8 @@ where
 
 impl<B, C1> IntoClassSet<B, ClassSet1<B, C1>> for C1
 where
-    B: UsbBus,
-    C1: UsbClass<B>,
+    B: UsbBus + Send,
+    C1: UsbClass<B> + Send,
 {
     fn into_class_set(self) -> ClassSet1<B, C1> {
         ClassSet1 {
@@ -210,9 +210,9 @@ where
 
 impl<B, C1, C2> IntoClassSet<B, ClassSet2<B, C1, C2>> for (C1, C2)
 where
-    B: UsbBus,
-    C1: UsbClass<B>,
-    C2: UsbClass<B>,
+    B: UsbBus + Send,
+    C1: UsbClass<B> + Send,
+    C2: UsbClass<B> + Send,
 {
     fn into_class_set(self) -> ClassSet2<B, C1, C2> {
         ClassSet2 {
diff --git a/embassy-nrf/src/timer.rs b/embassy-nrf/src/timer.rs
index a6e91f228..7ff35c320 100644
--- a/embassy-nrf/src/timer.rs
+++ b/embassy-nrf/src/timer.rs
@@ -29,7 +29,7 @@ pub(crate) mod sealed {
     pub trait ExtendedInstance {}
 }
 
-pub trait Instance: Unborrow<Target = Self> + sealed::Instance + 'static {
+pub trait Instance: Unborrow<Target = Self> + sealed::Instance + 'static + Send {
     type Interrupt: Interrupt;
 }
 pub trait ExtendedInstance: Instance + sealed::ExtendedInstance {}
diff --git a/embassy-nrf/src/uarte.rs b/embassy-nrf/src/uarte.rs
index 67ec5d73f..985854a5f 100644
--- a/embassy-nrf/src/uarte.rs
+++ b/embassy-nrf/src/uarte.rs
@@ -461,7 +461,7 @@ pub(crate) mod sealed {
     }
 }
 
-pub trait Instance: Unborrow<Target = Self> + sealed::Instance + 'static {
+pub trait Instance: Unborrow<Target = Self> + sealed::Instance + 'static + Send {
     type Interrupt: Interrupt;
 }
 
diff --git a/embassy/src/util/waker.rs b/embassy/src/util/waker.rs
index 393155099..1ac6054f9 100644
--- a/embassy/src/util/waker.rs
+++ b/embassy/src/util/waker.rs
@@ -48,6 +48,11 @@ impl WakerRegistration {
     }
 }
 
+// SAFETY: `WakerRegistration` effectively contains an `Option<Waker>`,
+// which is `Send` and `Sync`.
+unsafe impl Send for WakerRegistration {}
+unsafe impl Sync for WakerRegistration {}
+
 pub struct AtomicWaker {
     waker: AtomicPtr<TaskHeader>,
 }