diff --git a/x509-cert/src/serial_number.rs b/x509-cert/src/serial_number.rs
index 6aff10897..7897eface 100644
--- a/x509-cert/src/serial_number.rs
+++ b/x509-cert/src/serial_number.rs
@@ -12,7 +12,7 @@ use {
     core::ops::Add,
     generic_array::{
         typenum::{
-            consts::{self, U17, U19, U8},
+            consts::{U17, U19, U8},
             marker_traits::Unsigned,
             type_operators::{Max, Min},
             uint::UTerm,
@@ -88,71 +88,62 @@ impl<P: Profile> SerialNumber<P> {
     /// [ballot 164]: https://cabforum.org/2016/03/31/ballot-164/
     #[cfg(feature = "builder")]
     pub fn generate(rng: &mut impl CryptoRngCore) -> Result<Self> {
-        Self::generate_with_length::<U17>(rng)
+        Self::generate_with_prefix::<UTerm, U17>(GenericArray::default(), rng)
     }
 
-    /// Generates a random serial number from RNG.
+    /// Generates a random serial number from RNG. Include a prefix value.
     ///
     /// This follows the recommendation the CAB forum [ballot 164] and uses a minimum of 64 bits
     /// of output from the CSPRNG.
     ///
-    /// [ballot 164]: https://cabforum.org/2016/03/31/ballot-164/
-    #[cfg(feature = "builder")]
-    pub fn generate_with_length<N>(rng: &mut impl CryptoRngCore) -> Result<Self>
-    where
-        N: Unsigned + ArrayLength<u8>,
-        // Rand minimum is 64 bits
-        N: Min<U8>,
-        // Max length is 20 bytes, encoding of sign bit might
-        // requires an additional byte, so the limit is 19.
-        N: Max<U19>,
-    {
-        Self::generate_with_prefix::<UTerm, N>(GenericArray::default(), rng)
-    }
-
-    /// Generates a random serial number from RNG.
+    /// # Dynamic API
     ///
-    /// This follows the recommendation the CAB forum [ballot 164] and uses a minimum of 64 bits
-    /// of output from the CSPRNG.
-    ///
-    /// [ballot 164]: https://cabforum.org/2016/03/31/ballot-164/
-    #[cfg(feature = "builder")]
-    #[allow(unused_qualifications)]
-    pub fn generate_with_dyn_length(rng: &mut impl CryptoRngCore, len: usize) -> Result<Self> {
-        macro_rules! impl_generate {
-            ($len:literal => $u:ty) => {
-                if (len == $len) {
-                    return Self::generate_with_prefix::<UTerm, $u>(GenericArray::default(), rng);
-                }
-            };
-            ($len:literal => $u:ty, $($rest:tt)*) => {
-                impl_generate!($len => $u);
-                impl_generate!($($rest)*);
-            };
-        }
-
-        impl_generate!(
-            8 => consts::U8,
-            9 => consts::U9,
-            10 => consts::U10,
-            11 => consts::U11,
-            12 => consts::U12,
-            13 => consts::U13,
-            14 => consts::U14,
-            15 => consts::U15,
-            16 => consts::U16,
-            17 => consts::U17,
-            18 => consts::U18,
-            19 => consts::U19
-        );
-
-        Err(ErrorKind::Failed.into())
-    }
-
-    /// Generates a random serial number from RNG. Include a prefix value.
+    /// While this only provides a const-generic API. A dynamic generation can be implemented
+    /// like:
+    /// ```rust
+    /// use der::{ErrorKind, Result};
+    /// use generic_array::{
+    ///     typenum::{
+    ///         consts,
+    ///         uint::UTerm,
+    ///     },
+    ///     GenericArray,
+    /// };
+    /// use signature::rand_core::CryptoRngCore;
+    /// use x509_cert::serial_number::SerialNumber;
     ///
-    /// This follows the recommendation the CAB forum [ballot 164] and uses a minimum of 64 bits
-    /// of output from the CSPRNG.
+    /// /// Generates a random serial number from RNG.
+    /// n generate_with_dyn_length(rng: &mut impl CryptoRngCore, len: usize) -> Result<SerialNumber> {
+    ///     macro_rules! impl_generate {
+    ///         ($len:literal => $u:ty) => {
+    ///             if (len == $len) {
+    ///                 return SerialNumber::generate_with_prefix::<UTerm, $u>(GenericArray::default(), rng);
+    ///             }
+    ///         };
+    ///         ($len:literal => $u:ty, $($rest:tt)*) => {
+    ///             impl_generate!($len => $u);
+    ///             impl_generate!($($rest)*);
+    ///         };
+    ///     }
+
+    ///     impl_generate!(
+    ///         8 => consts::U8,
+    ///         9 => consts::U9,
+    ///         10 => consts::U10,
+    ///         11 => consts::U11,
+    ///         12 => consts::U12,
+    ///         13 => consts::U13,
+    ///         14 => consts::U14,
+    ///         15 => consts::U15,
+    ///         16 => consts::U16,
+    ///         17 => consts::U17,
+    ///         18 => consts::U18,
+    ///         19 => consts::U19
+    ///     );
+
+    ///     Err(ErrorKind::Failed.into())
+    /// }
+    /// ```
     ///
     /// [ballot 164]: https://cabforum.org/2016/03/31/ballot-164/
     #[cfg(feature = "builder")]