diff --git a/objc2/README.md b/objc2/README.md
index 90ced8f3f..354b4fed8 100644
--- a/objc2/README.md
+++ b/objc2/README.md
@@ -14,13 +14,13 @@ Objective-C objects can be messaged using the `msg_send!` macro:
 
 ```rust , no_run
 use objc2::{class, msg_send};
-use objc2::runtime::{BOOL, Object};
+use objc2::runtime::{Bool, Object};
 
 let cls = class!(NSObject);
 unsafe {
     let obj: *mut Object = msg_send![cls, new];
     let hash: usize = msg_send![obj, hash];
-    let is_kind: BOOL = msg_send![obj, isKindOfClass: cls];
+    let is_kind: Bool = msg_send![obj, isKindOfClass: cls];
     // Even void methods must have their return type annotated
     let _: () = msg_send![obj, release];
 }
diff --git a/objc2/src/bool.rs b/objc2/src/bool.rs
index 34065b277..d98bb79be 100644
--- a/objc2/src/bool.rs
+++ b/objc2/src/bool.rs
@@ -99,10 +99,21 @@ impl fmt::Debug for Bool {
     }
 }
 
+// SAFETY: `Bool` is `repr(transparent)`.
 unsafe impl Encode for Bool {
     const ENCODING: Encoding<'static> = objc2_sys::BOOL::ENCODING;
 }
 
+// Note that we shouldn't delegate to `BOOL`'s  `ENCODING_REF` since `BOOL` is
+// sometimes `i8`/`u8`, and their `ENCODING_REF`s are `Encoding::String`,
+// which is incorrect for `BOOL`:
+//
+// ```objc
+// @encode(BOOL); // -> "c", "C" or "B"
+// @encode(BOOL*); // -> "^c", "^C" or "^B"
+// @encode(char); // -> "c" or "C"
+// @encode(char*); // -> "*"
+// ```
 unsafe impl RefEncode for Bool {
     const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
 }
diff --git a/objc2/src/lib.rs b/objc2/src/lib.rs
index 50352b4aa..271c94148 100644
--- a/objc2/src/lib.rs
+++ b/objc2/src/lib.rs
@@ -7,12 +7,12 @@ Objective-C objects can be messaged using the [`msg_send!`](macro.msg_send!.html
 
 ``` no_run
 # use objc2::{class, msg_send};
-# use objc2::runtime::{BOOL, Class, Object};
+# use objc2::runtime::{Bool, Class, Object};
 # unsafe {
 let cls = class!(NSObject);
 let obj: *mut Object = msg_send![cls, new];
 let hash: usize = msg_send![obj, hash];
-let is_kind: BOOL = msg_send![obj, isKindOfClass: cls];
+let is_kind: Bool = msg_send![obj, isKindOfClass: cls];
 // Even void methods must have their return type annotated
 let _: () = msg_send![obj, release];
 # }
diff --git a/objc2/src/message/mod.rs b/objc2/src/message/mod.rs
index 9003b74e3..eb16d5d49 100644
--- a/objc2/src/message/mod.rs
+++ b/objc2/src/message/mod.rs
@@ -165,13 +165,13 @@ pub unsafe trait MessageReceiver: private::Sealed {
     /// # Example
     /// ``` no_run
     /// # use objc2::{class, msg_send, sel};
-    /// # use objc2::runtime::{BOOL, Class, Object};
+    /// # use objc2::runtime::{Bool, Class, Object};
     /// # use objc2::MessageReceiver;
     /// let obj: &Object;
     /// # obj = unsafe { msg_send![class!(NSObject), new] };
     /// let sel = sel!(isKindOfClass:);
     /// // Verify isKindOfClass: takes one Class and returns a BOOL
-    /// let result = obj.verify_message::<(&Class,), BOOL>(sel);
+    /// let result = obj.verify_message::<(&Class,), Bool>(sel);
     /// assert!(result.is_ok());
     /// ```
     fn verify_message<A, R>(&self, sel: Sel) -> Result<(), MessageError>
diff --git a/objc2_encode/src/encode.rs b/objc2_encode/src/encode.rs
index 8a371c642..a062cf084 100644
--- a/objc2_encode/src/encode.rs
+++ b/objc2_encode/src/encode.rs
@@ -1,4 +1,11 @@
-use core::{ffi::c_void, mem::ManuallyDrop, pin::Pin, ptr::NonNull};
+use core::ffi::c_void;
+use core::mem::ManuallyDrop;
+use core::num::{
+    NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize, NonZeroU16, NonZeroU32,
+    NonZeroU64, NonZeroU8, NonZeroUsize, Wrapping,
+};
+use core::pin::Pin;
+use core::ptr::NonNull;
 
 use crate::Encoding;
 
@@ -160,17 +167,22 @@ encode_impls!(
     u64 => ULongLong,
     f32 => Float,
     f64 => Double,
-    () => Void,
-    *mut i8 => String,
-    *const i8 => String,
-    *mut u8 => String,
-    *const u8 => String,
 );
 
+/// To allow usage as the return type of generic functions.
+///
+/// You should not rely on this encoding to exist for any other purpose (since
+/// `()` is not FFI-safe)!
+///
+/// TODO: Figure out a way to remove this.
+unsafe impl Encode for () {
+    const ENCODING: Encoding<'static> = Encoding::Void;
+}
+
 /// Using this directly is heavily discouraged, since the type of BOOL differs
 /// across platforms.
 ///
-/// Use `objc2_sys::BOOL::ENCODING` or `objc2::runtime::Bool` instead.
+/// Use `objc2::runtime::Bool::ENCODING` instead.
 unsafe impl Encode for bool {
     const ENCODING: Encoding<'static> = Encoding::Bool;
 }
@@ -194,16 +206,45 @@ encode_impls_size!(
     usize => (u16, u32, u64),
 );
 
-/// Simple helper for implementing [`Encode`] for integer types.
+/// Simple helper for implementing [`RefEncode`].
+macro_rules! pointer_refencode_impl {
+    ($($t:ty),*) => ($(
+        unsafe impl RefEncode for $t {
+            const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
+        }
+    )*);
+}
+
+pointer_refencode_impl!(bool, i16, i32, i64, isize, u16, u32, u64, usize, f32, f64);
+
+/// Pointers to [`i8`] use the special [`Encoding::String`] encoding.
+unsafe impl RefEncode for i8 {
+    const ENCODING_REF: Encoding<'static> = Encoding::String;
+}
+
+/// Pointers to [`u8`] use the special [`Encoding::String`] encoding.
+unsafe impl RefEncode for u8 {
+    const ENCODING_REF: Encoding<'static> = Encoding::String;
+}
+
+/// Simple helper for implementing [`Encode`] for nonzero integer types.
 macro_rules! encode_impls_nonzero {
     ($($nonzero:ident => $type:ty,)*) => ($(
-        unsafe impl Encode for core::num::$nonzero {
+        unsafe impl Encode for $nonzero {
             const ENCODING: Encoding<'static> = <$type>::ENCODING;
         }
 
-        unsafe impl Encode for Option<core::num::$nonzero> {
+        unsafe impl Encode for Option<$nonzero> {
             const ENCODING: Encoding<'static> = <$type>::ENCODING;
         }
+
+        unsafe impl RefEncode for $nonzero {
+            const ENCODING_REF: Encoding<'static> = <$type>::ENCODING_REF;
+        }
+
+        unsafe impl RefEncode for Option<$nonzero> {
+            const ENCODING_REF: Encoding<'static> = <$type>::ENCODING_REF;
+        }
     )*);
 }
 
@@ -229,12 +270,20 @@ unsafe impl Encode for *const c_void {
     const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Void);
 }
 
+unsafe impl RefEncode for *const c_void {
+    const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
+}
+
 /// [`Encode`] is implemented manually for `*mut c_void`, instead of
 /// implementing [`RefEncode`], to discourage creating `&mut c_void`.
 unsafe impl Encode for *mut c_void {
     const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Void);
 }
 
+unsafe impl RefEncode for *mut c_void {
+    const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
+}
+
 unsafe impl<T: Encode, const LENGTH: usize> Encode for [T; LENGTH] {
     const ENCODING: Encoding<'static> = Encoding::Array(LENGTH, &T::ENCODING);
 }
@@ -265,6 +314,16 @@ unsafe impl<T: RefEncode> RefEncode for Pin<T> {
     const ENCODING_REF: Encoding<'static> = T::ENCODING_REF;
 }
 
+// SAFETY: `Wrapping` is `repr(transparent)`.
+unsafe impl<T: Encode> Encode for Wrapping<T> {
+    const ENCODING: Encoding<'static> = T::ENCODING;
+}
+
+// SAFETY: `Wrapping` is `repr(transparent)`.
+unsafe impl<T: RefEncode> RefEncode for Wrapping<T> {
+    const ENCODING_REF: Encoding<'static> = T::ENCODING_REF;
+}
+
 /// Helper for implementing `Encode`/`RefEncode` for pointers to types that
 /// implement `RefEncode`.
 ///
@@ -423,3 +482,66 @@ encode_args_impl!(A, B, C, D, E, F, G, H, I);
 encode_args_impl!(A, B, C, D, E, F, G, H, I, J);
 encode_args_impl!(A, B, C, D, E, F, G, H, I, J, K);
 encode_args_impl!(A, B, C, D, E, F, G, H, I, J, K, L);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_c_string() {
+        assert_eq!(i8::ENCODING, Encoding::Char);
+        assert_eq!(u8::ENCODING, Encoding::UChar);
+
+        assert_eq!(<*const i8>::ENCODING, Encoding::String);
+        assert_eq!(<&u8>::ENCODING, Encoding::String);
+        assert_eq!(i8::ENCODING_REF, Encoding::String);
+        assert_eq!(i8::ENCODING_REF, Encoding::String);
+
+        assert_eq!(
+            <*const *const i8>::ENCODING,
+            Encoding::Pointer(&Encoding::String)
+        );
+        assert_eq!(<&&u8>::ENCODING, Encoding::Pointer(&Encoding::String));
+    }
+
+    #[test]
+    fn test_i32() {
+        assert_eq!(i32::ENCODING, Encoding::Int);
+        assert_eq!(<&i32>::ENCODING, Encoding::Pointer(&Encoding::Int));
+        assert_eq!(
+            <&&i32>::ENCODING,
+            Encoding::Pointer(&Encoding::Pointer(&Encoding::Int))
+        );
+    }
+
+    #[test]
+    fn test_void() {
+        // TODO: Remove this
+        assert_eq!(<()>::ENCODING, Encoding::Void);
+        assert_eq!(
+            <*const c_void>::ENCODING,
+            Encoding::Pointer(&Encoding::Void)
+        );
+        assert_eq!(
+            <&*const c_void>::ENCODING,
+            Encoding::Pointer(&Encoding::Pointer(&Encoding::Void))
+        );
+
+        // Shouldn't compile
+        // assert_eq!(<c_void>::ENCODING, Encoding::Void);
+        // assert_eq!(<*const ()>::ENCODING, Encoding::Pointer(&Encoding::Void));
+        // assert_eq!(<&c_void>::ENCODING, Encoding::Pointer(&Encoding::Void));
+    }
+
+    #[test]
+    fn test_extern_fn_pointer() {
+        assert_eq!(
+            <extern "C" fn()>::ENCODING,
+            Encoding::Pointer(&Encoding::Unknown)
+        );
+        assert_eq!(
+            <extern "C" fn(x: ()) -> ()>::ENCODING,
+            Encoding::Pointer(&Encoding::Unknown)
+        );
+    }
+}
diff --git a/objc2_sys/src/types.rs b/objc2_sys/src/types.rs
index 5a44e5ddb..c2d8c0e3d 100644
--- a/objc2_sys/src/types.rs
+++ b/objc2_sys/src/types.rs
@@ -65,6 +65,11 @@ mod inner {
 ///
 /// The type of this varies across platforms, so to convert an it into a Rust
 /// [`bool`], always compare it with [`YES`][`crate::YES`] or [`NO`][`crate::NO`].
+///
+/// Note that this type implements `objc2_encode::Encode` and
+/// `objc2_encode::RefEncode`, but the `RefEncode` implementation is wrong
+/// on some platforms! You should only use this on FFI boundaries, otherwise
+/// prefer `objc2::runtime::Bool`.
 pub type BOOL = inner::BOOL;
 
 /// An immutable pointer to a selector.