diff --git a/src/i2c.rs b/src/i2c.rs
index 9868155..1eb5b25 100644
--- a/src/i2c.rs
+++ b/src/i2c.rs
@@ -57,7 +57,7 @@ impl embedded_hal::i2c::Error for Error {
 }
 
 /// SDA pins
-pub trait SdaPin<I2C> : Sealed {}
+pub trait SdaPin<I2C>: Sealed {}
 
 /// SCL pins
 pub trait SclPin<I2C>: Sealed {}
diff --git a/src/serial.rs b/src/serial.rs
index a13f04c..8e9ce51 100644
--- a/src/serial.rs
+++ b/src/serial.rs
@@ -1,4 +1,5 @@
 //! Serial communication
+use self::private::Sealed;
 use crate::clock::Clocks;
 use crate::pac;
 use core::fmt;
@@ -349,27 +350,27 @@ where
 }
 
 /// Serial transmit pins - DO NOT IMPLEMENT THIS TRAIT
-pub unsafe trait TxPin<UART> {}
+pub trait TxPin<UART>: Sealed {}
 /// Serial receive pins - DO NOT IMPLEMENT THIS TRAIT
-pub unsafe trait RxPin<UART> {}
+pub trait RxPin<UART>: Sealed {}
 /// Serial rts pins - DO NOT IMPLEMENT THIS TRAIT
-pub unsafe trait RtsPin<UART> {}
+pub trait RtsPin<UART>: Sealed {}
 /// Serial cts pins - DO NOT IMPLEMENT THIS TRAIT
-pub unsafe trait CtsPin<UART> {}
+pub trait CtsPin<UART>: Sealed {}
 
 macro_rules! impl_uart_pin {
     ($(($UartSigi: ident, $UartMuxi: ident),)+) => {
         use crate::gpio::*;
         $(
-        unsafe impl<PIN: UartPin<$UartSigi>> TxPin<pac::UART0> for (PIN, $UartMuxi<Uart0Tx>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> RxPin<pac::UART0> for (PIN, $UartMuxi<Uart0Rx>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> RtsPin<pac::UART0> for (PIN, $UartMuxi<Uart0Rts>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> CtsPin<pac::UART0> for (PIN, $UartMuxi<Uart0Cts>) {}
-
-        unsafe impl<PIN: UartPin<$UartSigi>> TxPin<pac::UART1> for (PIN, $UartMuxi<Uart1Tx>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> RxPin<pac::UART1> for (PIN, $UartMuxi<Uart1Rx>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> RtsPin<pac::UART1> for (PIN, $UartMuxi<Uart1Rts>) {}
-        unsafe impl<PIN: UartPin<$UartSigi>> CtsPin<pac::UART1> for (PIN, $UartMuxi<Uart1Cts>) {}
+        impl<PIN: UartPin<$UartSigi>> TxPin<pac::UART0> for (PIN, $UartMuxi<Uart0Tx>) {}
+        impl<PIN: UartPin<$UartSigi>> RxPin<pac::UART0> for (PIN, $UartMuxi<Uart0Rx>) {}
+        impl<PIN: UartPin<$UartSigi>> RtsPin<pac::UART0> for (PIN, $UartMuxi<Uart0Rts>) {}
+        impl<PIN: UartPin<$UartSigi>> CtsPin<pac::UART0> for (PIN, $UartMuxi<Uart0Cts>) {}
+
+        impl<PIN: UartPin<$UartSigi>> TxPin<pac::UART1> for (PIN, $UartMuxi<Uart1Tx>) {}
+        impl<PIN: UartPin<$UartSigi>> RxPin<pac::UART1> for (PIN, $UartMuxi<Uart1Rx>) {}
+        impl<PIN: UartPin<$UartSigi>> RtsPin<pac::UART1> for (PIN, $UartMuxi<Uart1Rts>) {}
+        impl<PIN: UartPin<$UartSigi>> CtsPin<pac::UART1> for (PIN, $UartMuxi<Uart1Cts>) {}
         )+
     };
 }
@@ -416,3 +417,36 @@ where
     const HAS_RTS: bool = true;
     const HAS_CTS: bool = true;
 }
+
+// Prevent users from implementing the Serial pin traits
+mod private {
+    use crate::gpio;
+
+    pub trait Sealed {}
+    impl<TX, RX> Sealed for (TX, RX) {}
+    impl<TX, RX, RTS, CTS> Sealed for (TX, RX, RTS, CTS) {}
+
+    impl<MODE> Sealed for gpio::Pin0<MODE> {}
+    impl<MODE> Sealed for gpio::Pin1<MODE> {}
+    impl<MODE> Sealed for gpio::Pin2<MODE> {}
+    impl<MODE> Sealed for gpio::Pin3<MODE> {}
+    impl<MODE> Sealed for gpio::Pin4<MODE> {}
+    impl<MODE> Sealed for gpio::Pin5<MODE> {}
+    impl<MODE> Sealed for gpio::Pin6<MODE> {}
+    impl<MODE> Sealed for gpio::Pin7<MODE> {}
+    impl<MODE> Sealed for gpio::Pin8<MODE> {}
+    impl<MODE> Sealed for gpio::Pin9<MODE> {}
+    impl<MODE> Sealed for gpio::Pin10<MODE> {}
+    impl<MODE> Sealed for gpio::Pin11<MODE> {}
+    impl<MODE> Sealed for gpio::Pin12<MODE> {}
+    impl<MODE> Sealed for gpio::Pin13<MODE> {}
+    impl<MODE> Sealed for gpio::Pin14<MODE> {}
+    impl<MODE> Sealed for gpio::Pin15<MODE> {}
+    impl<MODE> Sealed for gpio::Pin16<MODE> {}
+    impl<MODE> Sealed for gpio::Pin17<MODE> {}
+    impl<MODE> Sealed for gpio::Pin18<MODE> {}
+    impl<MODE> Sealed for gpio::Pin19<MODE> {}
+    impl<MODE> Sealed for gpio::Pin20<MODE> {}
+    impl<MODE> Sealed for gpio::Pin21<MODE> {}
+    impl<MODE> Sealed for gpio::Pin22<MODE> {}
+}