diff --git a/num-format/src/buffer.rs b/num-format/src/buffer.rs
index c600d35..30eb307 100644
--- a/num-format/src/buffer.rs
+++ b/num-format/src/buffer.rs
@@ -78,7 +78,7 @@ impl Buffer {
     #[inline(always)]
     pub fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> usize
     where
-        F: Format,
+        F: Format + ?Sized,
         N: ToFormattedStr,
     {
         n.read_to_buffer(self, format)
diff --git a/num-format/src/custom_format_builder.rs b/num-format/src/custom_format_builder.rs
index 5d515f6..db18d42 100644
--- a/num-format/src/custom_format_builder.rs
+++ b/num-format/src/custom_format_builder.rs
@@ -70,7 +70,7 @@ impl CustomFormatBuilder {
     /// Sets all fields based on the provided format.
     pub fn format<F>(mut self, value: &F) -> Self
     where
-        F: Format,
+        F: Format + ?Sized,
     {
         self.dec = DecString::new(value.decimal());
         self.grp = value.grouping();
diff --git a/num-format/src/impls/integers.rs b/num-format/src/impls/integers.rs
index 64c273e..d7dad4a 100644
--- a/num-format/src/impls/integers.rs
+++ b/num-format/src/impls/integers.rs
@@ -18,7 +18,7 @@ impl ToFormattedStr for u8 {
     #[inline(always)]
     fn read_to_buffer<'a, F>(&self, buf: &'a mut Buffer, _: &F) -> usize
     where
-        F: Format,
+        F: Format + ?Sized,
     {
         buf.write_with_itoa(*self)
     }
@@ -31,7 +31,7 @@ macro_rules! impl_unsigned {
             #[inline(always)]
             fn read_to_buffer<'a, F>(&self, buf: &'a mut Buffer, format: &F) -> usize
             where
-                F: Format,
+                F: Format + ?Sized,
             {
                 let n = *self as u128;
                 run_core_algorithm(n, buf, format)
@@ -62,7 +62,7 @@ macro_rules! impl_signed {
             #[inline(always)]
             fn read_to_buffer<'a, F>(&self, buf: &'a mut Buffer, format: &F) -> usize
             where
-                F: Format,
+                F: Format + ?Sized,
             {
                 if self.is_negative() {
                     let n = (!(*self as u128)).wrapping_add(1); // make positive by adding 1 to the 2s complement
@@ -105,7 +105,7 @@ impl ToFormattedStr for NonZeroU8 {
     #[inline(always)]
     fn read_to_buffer<'a, F>(&self, buf: &'a mut Buffer, _: &F) -> usize
     where
-        F: Format,
+        F: Format + ?Sized,
     {
         buf.write_with_itoa(self.get())
     }
@@ -118,7 +118,7 @@ macro_rules! impl_non_zero {
             #[inline(always)]
             fn read_to_buffer<'a, F>(&self, buf: &'a mut Buffer, format: &F) -> usize
             where
-                F: Format,
+                F: Format + ?Sized,
             {
                 let n = self.get() as u128;
                 run_core_algorithm(n, buf, format)
@@ -145,7 +145,7 @@ impl Sealed for NonZeroU128 {}
 #[inline(always)]
 fn run_core_algorithm<F>(mut n: u128, buf: &mut Buffer, format: &F) -> usize
 where
-    F: Format,
+    F: Format + ?Sized,
 {
     // Bail out early if we can just use itoa
     // (i.e. if we don't have a separator)
diff --git a/num-format/src/impls/num.rs b/num-format/src/impls/num.rs
index 568b103..ffbfcc5 100644
--- a/num-format/src/impls/num.rs
+++ b/num-format/src/impls/num.rs
@@ -13,7 +13,7 @@ impl ToFormattedString for BigInt {
     #[inline(always)]
     fn read_to_io_writer<F, W>(&self, mut w: W, format: &F) -> Result<usize, io::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: io::Write,
     {
         match self.sign() {
@@ -35,7 +35,7 @@ impl ToFormattedString for BigInt {
     #[inline(always)]
     fn read_to_fmt_writer<F, W>(&self, mut w: W, format: &F) -> Result<usize, fmt::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: fmt::Write,
     {
         match self.sign() {
@@ -59,7 +59,7 @@ impl ToFormattedString for BigUint {
     #[inline(always)]
     fn read_to_io_writer<F, W>(&self, w: W, format: &F) -> Result<usize, io::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: io::Write,
     {
         let s = self.to_string();
@@ -70,7 +70,7 @@ impl ToFormattedString for BigUint {
     #[inline(always)]
     fn read_to_fmt_writer<F, W>(&self, w: W, format: &F) -> Result<usize, fmt::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: fmt::Write,
     {
         let s = self.to_string();
@@ -86,7 +86,7 @@ impl Sealed for BigUint {}
 fn io_algorithm<F, W>(s: String, mut w: W, format: &F) -> Result<usize, io::Error>
 where
     W: io::Write,
-    F: Format,
+    F: Format + ?Sized,
 {
     let separator = format.separator().into_str();
     let grouping = format.grouping();
@@ -146,7 +146,7 @@ where
 fn fmt_algorithm<F, W>(s: String, mut w: W, format: &F) -> Result<usize, fmt::Error>
 where
     W: fmt::Write,
-    F: Format,
+    F: Format + ?Sized,
 {
     let separator = format.separator().into_str();
     let grouping = format.grouping();
diff --git a/num-format/src/parsing.rs b/num-format/src/parsing.rs
index 71e992b..9e29bc9 100644
--- a/num-format/src/parsing.rs
+++ b/num-format/src/parsing.rs
@@ -42,7 +42,7 @@ pub trait ParseFormatted {
     /// [Examples]: trait.ParseFormatted.html#examples
     fn parse_formatted<F, N>(&self, format: &F) -> Result<N, Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         N: FromFormattedStr;
 }
 
@@ -52,7 +52,7 @@ where
 {
     fn parse_formatted<F, N>(&self, format: &F) -> Result<N, Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         N: FromFormattedStr,
     {
         FromFormattedStr::from_formatted_str(self.as_ref(), format)
@@ -69,7 +69,7 @@ pub trait FromFormattedStr: Sealed + Sized {
     #[allow(missing_docs)]
     fn from_formatted_str<F>(s: &str, format: &F) -> Result<Self, Error>
     where
-        F: Format;
+        F: Format + ?Sized;
 }
 
 macro_rules! impl_from_formatted_str {
@@ -77,7 +77,7 @@ macro_rules! impl_from_formatted_str {
         impl FromFormattedStr for $type {
             fn from_formatted_str<F>(s: &str, format: &F) -> Result<Self, Error>
             where
-                F: Format,
+                F: Format + ?Sized,
             {
                 const BUF_LEN: usize = $max_len;
                 let mut buf: [u8; BUF_LEN] = [0; BUF_LEN];
@@ -132,7 +132,7 @@ macro_rules! impl_from_formatted_str_non_zero {
         impl FromFormattedStr for $type {
             fn from_formatted_str<F>(s: &str, format: &F) -> Result<Self, Error>
             where
-                F: Format,
+                F: Format + ?Sized,
             {
                 let n = s.parse_formatted::<_, $related_type>(format)?;
                 let n = Self::new(n).ok_or_else(|| Error::parse_number(s))?;
@@ -160,7 +160,7 @@ mod num {
             impl FromFormattedStr for $type {
                 fn from_formatted_str<F>(s: &str, format: &F) -> Result<Self, Error>
                 where
-                    F: Format,
+                    F: Format + ?Sized,
                 {
                     let mut buf = Vec::new();
 
diff --git a/num-format/src/to_formatted_str.rs b/num-format/src/to_formatted_str.rs
index ed98871..e26dc62 100644
--- a/num-format/src/to_formatted_str.rs
+++ b/num-format/src/to_formatted_str.rs
@@ -11,5 +11,5 @@ pub trait ToFormattedStr: Sealed + Sized {
     #[doc(hidden)]
     fn read_to_buffer<F>(&self, buf: &mut Buffer, format: &F) -> usize
     where
-        F: Format;
+        F: Format + ?Sized;
 }
diff --git a/num-format/src/to_formatted_string.rs b/num-format/src/to_formatted_string.rs
index 2db4c0b..af9f539 100644
--- a/num-format/src/to_formatted_string.rs
+++ b/num-format/src/to_formatted_string.rs
@@ -16,19 +16,19 @@ pub trait ToFormattedString: Sealed + Sized {
     #[doc(hidden)]
     fn read_to_fmt_writer<F, W>(&self, w: W, format: &F) -> Result<usize, fmt::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: fmt::Write;
 
     #[doc(hidden)]
     fn read_to_io_writer<F, W>(&self, w: W, format: &F) -> Result<usize, io::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: io::Write;
 
     /// Returns a string representation of the number formatted according to the provided format.
     fn to_formatted_string<F>(&self, format: &F) -> String
     where
-        F: Format,
+        F: Format + ?Sized,
     {
         let mut s = String::with_capacity(MAX_BUF_LEN);
         let _ = self.read_to_fmt_writer(&mut s, format).unwrap();
@@ -43,7 +43,7 @@ where
     #[inline(always)]
     fn read_to_fmt_writer<F, W>(&self, mut w: W, format: &F) -> Result<usize, fmt::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: fmt::Write,
     {
         let mut buf = Buffer::default();
@@ -55,7 +55,7 @@ where
     #[inline(always)]
     fn read_to_io_writer<F, W>(&self, mut w: W, format: &F) -> Result<usize, io::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         W: io::Write,
     {
         let mut buf = Buffer::default();
diff --git a/num-format/src/write_formatted.rs b/num-format/src/write_formatted.rs
index 9245f2e..68c5179 100644
--- a/num-format/src/write_formatted.rs
+++ b/num-format/src/write_formatted.rs
@@ -28,7 +28,7 @@ pub trait WriteFormatted {
     /// [`write_str`]: https://doc.rust-lang.org/stable/std/fmt/trait.Write.html#tymethod.write_str
     fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, io::Error>
     where
-        F: Format,
+        F: Format + ?Sized,
         N: ToFormattedString;
 }
 
@@ -37,7 +37,7 @@ macro_rules! impl_for_fmt_write {
         #[inline(always)]
         fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, io::Error>
         where
-            F: Format,
+            F: Format + ?Sized,
             N: ToFormattedString,
         {
             n.read_to_fmt_writer(self, format)
@@ -51,7 +51,7 @@ macro_rules! impl_for_io_write {
         #[inline(always)]
         fn write_formatted<F, N>(&mut self, n: &N, format: &F) -> Result<usize, io::Error>
         where
-            F: Format,
+            F: Format + ?Sized,
             N: ToFormattedString,
         {
             n.read_to_io_writer(self, format)