Move error types to error submodules

diff --git a/bitcoin/src/merkle_tree/mod.rs b/bitcoin/src/merkle_tree/mod.rs
index 121e0931..47feb480 100644
--- a/bitcoin/src/merkle_tree/mod.rs
+++ b/bitcoin/src/merkle_tree/mod.rs
@@ -18,4 +18,10 @@
 #[doc(inline)]
 pub use primitives::merkle_tree::{TxMerkleNodeDecoder, TxMerkleNodeEncoder, TxMerkleNode, WitnessMerkleNode};
 #[doc(no_inline)]
-pub use primitives::merkle_tree::TxMerkleNodeDecoderError;
+pub use self::error::TxMerkleNodeDecoderError;
+
+/// Error types for the merkle tree module.
+pub mod error {
+    #[doc(inline)]
+    pub use primitives::merkle_tree::TxMerkleNodeDecoderError;
+}
diff --git a/primitives/src/merkle_tree.rs b/primitives/src/merkle_tree.rs
index fcf0ba99..eca3de5a 100644
--- a/primitives/src/merkle_tree.rs
+++ b/primitives/src/merkle_tree.rs
@@ -16,10 +16,11 @@ use hashes::{sha256d, HashEngine};
 #[cfg(not(feature = "alloc"))]
 use internals::array_vec::ArrayVec;
 
+#[doc(no_inline)]
+pub use self::error::TxMerkleNodeDecoderError;
 #[doc(inline)]
 pub use crate::hash_types::{
-    TxMerkleNode, TxMerkleNodeDecoder, TxMerkleNodeDecoderError, TxMerkleNodeEncoder,
-    WitnessMerkleNode,
+    TxMerkleNode, TxMerkleNodeDecoder, TxMerkleNodeEncoder, WitnessMerkleNode,
 };
 use crate::hash_types::{Txid, Wtxid};
 use crate::transaction::TxIdentifier;
@@ -194,6 +195,12 @@ impl MerkleNode for WitnessMerkleNode {
     }
 }
 
+/// Error types for the merkle tree module.
+pub mod error {
+    #[doc(inline)]
+    pub use crate::hash_types::TxMerkleNodeDecoderError;
+}
+
 #[cfg(test)]
 mod tests {
     use hashes::HashEngine;
diff --git a/units/src/fee_rate/serde.rs b/units/src/fee_rate/serde.rs
index 1ba3e12a..9b184c5d 100644
--- a/units/src/fee_rate/serde.rs
+++ b/units/src/fee_rate/serde.rs
@@ -23,8 +23,8 @@
 //! }
 //! ```
 
-use core::convert::Infallible;
-use core::fmt;
+#[doc(no_inline)]
+pub use self::error::OverflowError;
 
 pub mod as_sat_per_kwu_floor {
     //! Serialize and deserialize [`FeeRate`] denominated in satoshis per 1000 weight units.
@@ -406,26 +406,32 @@ pub mod as_sat_per_vb_ceil {
     }
 }
 
-/// Overflow occurred while deserializing fee rate per virtual byte.
-#[derive(Debug, Clone, PartialEq, Eq)]
-#[non_exhaustive]
-pub struct OverflowError;
+/// Error types for fee rate serde handling.
+pub mod error {
+    use core::convert::Infallible;
+    use core::fmt;
 
-impl From<Infallible> for OverflowError {
-    fn from(never: Infallible) -> Self { match never {} }
-}
+    /// Overflow occurred while deserializing fee rate per virtual byte.
+    #[derive(Debug, Clone, PartialEq, Eq)]
+    #[non_exhaustive]
+    pub struct OverflowError;
 
-impl fmt::Display for OverflowError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "overflow occurred while deserializing fee rate per virtual byte")
+    impl From<Infallible> for OverflowError {
+        fn from(never: Infallible) -> Self { match never {} }
     }
-}
 
-#[cfg(feature = "std")]
-impl std::error::Error for OverflowError {
-    #[inline]
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        let Self {} = self;
-        None
+    impl fmt::Display for OverflowError {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "overflow occurred while deserializing fee rate per virtual byte")
+        }
+    }
+
+    #[cfg(feature = "std")]
+    impl std::error::Error for OverflowError {
+        #[inline]
+        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+            let Self {} = self;
+            None
+        }
     }
 }