diff --git a/src/ext/mod.rs b/src/ext/mod.rs
index b59d809dea..a349121ff9 100644
--- a/src/ext/mod.rs
+++ b/src/ext/mod.rs
@@ -42,8 +42,12 @@ use bytes::Bytes;
     feature = "ffi"
 ))]
 use http::header::HeaderName;
+#[cfg(all(feature = "http1", feature = "ffi"))]
+use http::header::IntoHeaderName;
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+use http::header::InvalidHeaderName;
 #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
-use http::header::{HeaderMap, IntoHeaderName, ValueIter};
+use http::header::{HeaderMap, ValueIter};
 #[cfg(feature = "ffi")]
 use std::collections::HashMap;
 #[cfg(feature = "http2")]
@@ -157,15 +161,15 @@ impl fmt::Debug for Protocol {
 ///
 /// [`preserve_header_case`]: /client/struct.Client.html#method.preserve_header_case
 #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
-#[derive(Clone, Debug)]
-pub(crate) struct HeaderCaseMap(HeaderMap<Bytes>);
+#[derive(Clone, Debug, Default)]
+pub struct HeaderCaseMap(HeaderMap<Bytes>);
 
 #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
 impl HeaderCaseMap {
     /// Returns a view of all spellings associated with that header name,
     /// in the order they were found.
     #[cfg(feature = "client")]
-    pub(crate) fn get_all<'a>(
+    pub fn get_all<'a>(
         &'a self,
         name: &HeaderName,
     ) -> impl Iterator<Item = impl AsRef<[u8]> + 'a> + 'a {
@@ -179,22 +183,62 @@ impl HeaderCaseMap {
         self.0.get_all(name).into_iter()
     }
 
-    #[cfg(any(feature = "client", feature = "server"))]
-    pub(crate) fn default() -> Self {
-        Self(Default::default())
+    /// Inserts a header spelling, replacing any existing ones associated with that header name.
+    #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+    pub fn insert(&mut self, name: CasedHeaderName) {
+        self.0.insert(name.0, name.1);
     }
 
-    #[cfg(any(test, feature = "ffi"))]
-    pub(crate) fn insert(&mut self, name: HeaderName, orig: Bytes) {
-        self.0.insert(name, orig);
+    /// Inserts a header spelling in addition to any existing ones associated with that header name.
+    #[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+    pub fn append(&mut self, name: CasedHeaderName) {
+        self.0.append(name.0, name.1);
     }
+}
 
-    #[cfg(any(feature = "client", feature = "server"))]
-    pub(crate) fn append<N>(&mut self, name: N, orig: Bytes)
-    where
-        N: IntoHeaderName,
-    {
-        self.0.append(name, orig);
+/// An error converting a header name spelling to a [`CasedHeaderName`].
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+#[derive(Debug)]
+pub enum CasedHeaderNameError {
+    /// Error parsing the header name
+    Invalid(InvalidHeaderName),
+    /// The parsed header name doesn't match the spelling's
+    NoMatch,
+}
+
+/// A header casing representation, guaranteed to be a valid [`http::HeaderName`].
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+#[derive(Debug)]
+pub struct CasedHeaderName(HeaderName, Bytes);
+
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+impl CasedHeaderName {
+    /// Constructs a header casing representation.
+    pub fn new(name: HeaderName, orig: Bytes) -> Result<Self, CasedHeaderNameError> {
+        let orig_parsed =
+            HeaderName::from_bytes(&orig).map_err(|err| CasedHeaderNameError::Invalid(err))?;
+
+        if orig_parsed != name {
+            Err(CasedHeaderNameError::NoMatch)
+        } else {
+            Ok(CasedHeaderName(name.into(), orig))
+        }
+    }
+}
+
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+impl TryFrom<Bytes> for CasedHeaderName {
+    type Error = InvalidHeaderName;
+
+    fn try_from(orig: Bytes) -> Result<Self, Self::Error> {
+        HeaderName::from_bytes(&orig).map(|name| CasedHeaderName(name, orig))
+    }
+}
+
+#[cfg(all(any(feature = "client", feature = "server"), feature = "http1"))]
+impl From<CasedHeaderName> for HeaderName {
+    fn from(value: CasedHeaderName) -> Self {
+        value.0
     }
 }
 
diff --git a/src/ffi/http_types.rs b/src/ffi/http_types.rs
index 3dc4a2549d..264f7a56fa 100644
--- a/src/ffi/http_types.rs
+++ b/src/ffi/http_types.rs
@@ -7,7 +7,7 @@ use super::error::hyper_code;
 use super::task::{hyper_task_return_type, AsTaskType};
 use super::{UserDataPointer, HYPER_ITER_CONTINUE};
 use crate::body::Incoming as IncomingBody;
-use crate::ext::{HeaderCaseMap, OriginalHeaderOrder, ReasonPhrase};
+use crate::ext::{CasedHeaderName, HeaderCaseMap, OriginalHeaderOrder, ReasonPhrase};
 use crate::ffi::size_t;
 use crate::header::{HeaderName, HeaderValue};
 use crate::{HeaderMap, Method, Request, Response, Uri};
@@ -513,7 +513,7 @@ ffi_fn! {
         match unsafe { raw_name_value(name, name_len, value, value_len) } {
             Ok((name, value, orig_name)) => {
                 headers.headers.insert(&name, value);
-                headers.orig_casing.insert(name.clone(), orig_name.clone());
+                headers.orig_casing.insert(CasedHeaderName::new(name.clone(), orig_name).unwrap()).unwrap();
                 headers.orig_order.insert(name);
                 hyper_code::HYPERE_OK
             }
@@ -533,7 +533,7 @@ ffi_fn! {
         match unsafe { raw_name_value(name, name_len, value, value_len) } {
             Ok((name, value, orig_name)) => {
                 headers.headers.append(&name, value);
-                headers.orig_casing.append(&name, orig_name.clone());
+                headers.orig_casing.append(CasedHeaderName::new(name.clone(), orig_name).unwrap()).unwrap();
                 headers.orig_order.append(name);
                 hyper_code::HYPERE_OK
             }
diff --git a/src/proto/h1/role.rs b/src/proto/h1/role.rs
index 1674e26bc6..3f4cc77c25 100644
--- a/src/proto/h1/role.rs
+++ b/src/proto/h1/role.rs
@@ -315,7 +315,12 @@ impl Http1Transaction for Server {
             }
 
             if let Some(ref mut header_case_map) = header_case_map {
-                header_case_map.append(&name, slice.slice(header.name.0..header.name.1));
+                use crate::ext::CasedHeaderName;
+
+                header_case_map.append(
+                    CasedHeaderName::new(name.clone(), slice.slice(header.name.0..header.name.1))
+                        .unwrap(),
+                );
             }
 
             #[cfg(feature = "ffi")]
@@ -1106,7 +1111,15 @@ impl Http1Transaction for Client {
                 }
 
                 if let Some(ref mut header_case_map) = header_case_map {
-                    header_case_map.append(&name, slice.slice(header.name.0..header.name.1));
+                    use crate::ext::CasedHeaderName;
+
+                    header_case_map.append(
+                        CasedHeaderName::new(
+                            name.clone(),
+                            slice.slice(header.name.0..header.name.1),
+                        )
+                        .unwrap(),
+                    );
                 }
 
                 #[cfg(feature = "ffi")]
@@ -1641,6 +1654,8 @@ fn extend(dst: &mut Vec<u8>, data: &[u8]) {
 mod tests {
     use bytes::BytesMut;
 
+    use crate::ext::CasedHeaderName;
+
     use super::*;
 
     #[cfg(feature = "server")]
@@ -2487,7 +2502,7 @@ mod tests {
             .insert("content-type", HeaderValue::from_static("application/json"));
 
         let mut orig_headers = HeaderCaseMap::default();
-        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        orig_headers.insert(CasedHeaderName::new(CONTENT_LENGTH, "CONTENT-LENGTH".into()).unwrap());
         head.extensions.insert(orig_headers);
 
         let mut vec = Vec::new();
@@ -2524,7 +2539,7 @@ mod tests {
             .insert("content-type", HeaderValue::from_static("application/json"));
 
         let mut orig_headers = HeaderCaseMap::default();
-        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        orig_headers.insert(CasedHeaderName::new(CONTENT_LENGTH, "CONTENT-LENGTH".into()).unwrap());
         head.extensions.insert(orig_headers);
 
         let mut vec = Vec::new();
@@ -2619,7 +2634,7 @@ mod tests {
             .insert("content-type", HeaderValue::from_static("application/json"));
 
         let mut orig_headers = HeaderCaseMap::default();
-        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        orig_headers.insert(CasedHeaderName::new(CONTENT_LENGTH, "CONTENT-LENGTH".into()).unwrap());
         head.extensions.insert(orig_headers);
 
         let mut vec = Vec::new();
@@ -2655,7 +2670,7 @@ mod tests {
             .insert("content-type", HeaderValue::from_static("application/json"));
 
         let mut orig_headers = HeaderCaseMap::default();
-        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        orig_headers.insert(CasedHeaderName::new(CONTENT_LENGTH, "CONTENT-LENGTH".into()).unwrap());
         head.extensions.insert(orig_headers);
 
         let mut vec = Vec::new();
@@ -2692,7 +2707,7 @@ mod tests {
             .insert("content-type", HeaderValue::from_static("application/json"));
 
         let mut orig_headers = HeaderCaseMap::default();
-        orig_headers.insert(CONTENT_LENGTH, "CONTENT-LENGTH".into());
+        orig_headers.insert(CasedHeaderName::new(CONTENT_LENGTH, "CONTENT-LENGTH".into()).unwrap());
         head.extensions.insert(orig_headers);
 
         let mut vec = Vec::new();
@@ -2897,7 +2912,7 @@ mod tests {
         let name = http::header::HeaderName::from_static("x-empty");
         headers.insert(&name, "".parse().expect("parse empty"));
         let mut orig_cases = HeaderCaseMap::default();
-        orig_cases.insert(name, Bytes::from_static(b"X-EmptY"));
+        orig_cases.insert(CasedHeaderName::new(name, Bytes::from_static(b"X-EmptY")).unwrap());
 
         let mut dst = Vec::new();
         super::write_headers_original_case(&headers, &orig_cases, &mut dst, false);
@@ -2916,8 +2931,9 @@ mod tests {
         headers.append(&name, "b".parse().unwrap());
 
         let mut orig_cases = HeaderCaseMap::default();
-        orig_cases.insert(name.clone(), Bytes::from_static(b"X-Empty"));
-        orig_cases.append(name, Bytes::from_static(b"X-EMPTY"));
+        orig_cases
+            .insert(CasedHeaderName::new(name.clone(), Bytes::from_static(b"X-Empty")).unwrap());
+        orig_cases.append(CasedHeaderName::new(name, Bytes::from_static(b"X-EMPTY")).unwrap());
 
         let mut dst = Vec::new();
         super::write_headers_original_case(&headers, &orig_cases, &mut dst, false);