diff --git a/embassy-stm32/src/spi/mod.rs b/embassy-stm32/src/spi/mod.rs
index 3e00fdd4e..79dce3306 100644
--- a/embassy-stm32/src/spi/mod.rs
+++ b/embassy-stm32/src/spi/mod.rs
@@ -6,6 +6,8 @@ mod spi;
 
 pub use spi::*;
 
+use crate::gpio::Pin;
+
 pub enum Error {
     Framing,
     Crc,
@@ -41,32 +43,21 @@ impl Default for Config {
 
 pub(crate) mod sealed {
     use super::*;
-    use crate::gpio::Pin;
-    use embassy::util::AtomicWaker;
 
     pub trait Instance {
         fn regs() -> &'static crate::pac::spi::Spi;
     }
 
     pub trait SckPin<T: Instance>: Pin {
-        const AF: u8;
-        fn af(&self) -> u8 {
-            Self::AF
-        }
+        fn af_num(&self) -> u8;
     }
 
     pub trait MosiPin<T: Instance>: Pin {
-        const AF: u8;
-        fn af(&self) -> u8 {
-            Self::AF
-        }
+        fn af_num(&self) -> u8;
     }
 
     pub trait MisoPin<T: Instance>: Pin {
-        const AF: u8;
-        fn af(&self) -> u8 {
-            Self::AF
-        }
+        fn af_num(&self) -> u8;
     }
 }
 
@@ -95,7 +86,9 @@ macro_rules! impl_spi_pin {
         impl crate::spi::$pin_func<peripherals::$inst> for peripherals::$pin {}
 
         impl crate::spi::sealed::$pin_func<peripherals::$inst> for peripherals::$pin {
-            const AF: u8 = $af;
+            fn af_num(&self) -> u8 {
+                $af
+            }
         }
     };
 }
diff --git a/embassy-stm32/src/spi/spi_v1.rs b/embassy-stm32/src/spi/spi_v1.rs
index 90515727f..a464c4275 100644
--- a/embassy-stm32/src/spi/spi_v1.rs
+++ b/embassy-stm32/src/spi/spi_v1.rs
@@ -43,9 +43,9 @@ impl<'d, T: Instance> Spi<'d, T> {
         unborrow!(peri, sck, mosi, miso);
 
         unsafe {
-            sck.set_as_af(sck.af());
-            mosi.set_as_af(mosi.af());
-            miso.set_as_af(miso.af());
+            sck.set_as_af(sck.af_num());
+            mosi.set_as_af(mosi.af_num());
+            miso.set_as_af(miso.af_num());
         }
 
         let sck = sck.degrade();
diff --git a/embassy-stm32/src/usart.rs b/embassy-stm32/src/usart.rs
index a49383bc9..e4f77398f 100644
--- a/embassy-stm32/src/usart.rs
+++ b/embassy-stm32/src/usart.rs
@@ -56,20 +56,20 @@ pub(crate) mod sealed {
     pub trait Instance {
         fn regs(&self) -> Usart;
     }
-    pub trait RxPin<T: Instance>: OptionalPin {
-        const AF_NUM: u8;
+    pub trait RxPin<T: Instance>: Pin {
+        fn af_num(&self) -> u8;
     }
-    pub trait TxPin<T: Instance>: OptionalPin {
-        const AF_NUM: u8;
+    pub trait TxPin<T: Instance>: Pin {
+        fn af_num(&self) -> u8;
     }
-    pub trait CtsPin<T: Instance>: OptionalPin {
-        const AF_NUM: u8;
+    pub trait CtsPin<T: Instance>: Pin {
+        fn af_num(&self) -> u8;
     }
-    pub trait RtsPin<T: Instance>: OptionalPin {
-        const AF_NUM: u8;
+    pub trait RtsPin<T: Instance>: Pin {
+        fn af_num(&self) -> u8;
     }
-    pub trait CkPin<T: Instance>: OptionalPin {
-        const AF_NUM: u8;
+    pub trait CkPin<T: Instance>: Pin {
+        fn af_num(&self) -> u8;
     }
 }
 pub trait Instance: sealed::Instance {}
@@ -79,27 +79,6 @@ pub trait CtsPin<T: Instance>: sealed::CtsPin<T> {}
 pub trait RtsPin<T: Instance>: sealed::RtsPin<T> {}
 pub trait CkPin<T: Instance>: sealed::CkPin<T> {}
 
-impl<T: Instance> sealed::RxPin<T> for NoPin {
-    const AF_NUM: u8 = 0;
-}
-impl<T: Instance> RxPin<T> for NoPin {}
-impl<T: Instance> sealed::TxPin<T> for NoPin {
-    const AF_NUM: u8 = 0;
-}
-impl<T: Instance> TxPin<T> for NoPin {}
-impl<T: Instance> sealed::CtsPin<T> for NoPin {
-    const AF_NUM: u8 = 0;
-}
-impl<T: Instance> CtsPin<T> for NoPin {}
-impl<T: Instance> sealed::RtsPin<T> for NoPin {
-    const AF_NUM: u8 = 0;
-}
-impl<T: Instance> RtsPin<T> for NoPin {}
-impl<T: Instance> sealed::CkPin<T> for NoPin {
-    const AF_NUM: u8 = 0;
-}
-impl<T: Instance> CkPin<T> for NoPin {}
-
 macro_rules! impl_usart {
     ($inst:ident) => {
         impl crate::usart::sealed::Instance for peripherals::$inst {
@@ -112,9 +91,11 @@ macro_rules! impl_usart {
 }
 
 macro_rules! impl_usart_pin {
-    ($inst:ident, $func:ident, $pin:ident, $num:expr) => {
+    ($inst:ident, $func:ident, $pin:ident, $af:expr) => {
         impl crate::usart::sealed::$func<peripherals::$inst> for peripherals::$pin {
-            const AF_NUM: u8 = $num;
+            fn af_num(&self) -> u8 {
+                $af
+            }
         }
         impl crate::usart::$func<peripherals::$inst> for peripherals::$pin {}
     };