diff --git a/crates/trusted-server-core/src/host_rewrite.rs b/crates/trusted-server-core/src/host_rewrite.rs
index cb15f407..dbae4668 100644
--- a/crates/trusted-server-core/src/host_rewrite.rs
+++ b/crates/trusted-server-core/src/host_rewrite.rs
@@ -1,6 +1,9 @@
 /// Rewrite bare host occurrences (e.g. `origin.example.com/news`) only when the match is a full
 /// hostname token, not part of a larger hostname like `cdn.origin.example.com`.
 ///
+/// A numeric `:port` immediately after the host is treated as part of a standalone authority and
+/// is preserved when rewriting the host.
+///
 /// This is used by both HTML (`__next_f` payloads) and Flight (`text/x-component`) rewriting to
 /// avoid corrupting unrelated hostnames.
 pub(crate) fn rewrite_bare_host_at_boundaries(
@@ -16,6 +19,15 @@ pub(crate) fn rewrite_bare_host_at_boundaries(
         byte.is_ascii_alphanumeric() || matches!(byte, b'.' | b'-' | b':')
     }
 
+    fn has_valid_port_boundary(bytes: &[u8], port_start: usize) -> bool {
+        let mut index = port_start;
+        while index < bytes.len() && bytes[index].is_ascii_digit() {
+            index += 1;
+        }
+
+        index > port_start && (index == bytes.len() || !is_host_char(bytes[index]))
+    }
+
     let origin_len = origin_host.len();
     let bytes = text.as_bytes();
     let mut out = String::with_capacity(text.len());
@@ -27,7 +39,12 @@ pub(crate) fn rewrite_bare_host_at_boundaries(
         let end = pos + origin_len;
 
         let before_ok = pos == 0 || !is_host_char(bytes[pos - 1]);
-        let after_ok = end == bytes.len() || !is_host_char(bytes[end]);
+        let after_ok = end == bytes.len()
+            || if bytes[end] == b':' {
+                has_valid_port_boundary(bytes, end + 1)
+            } else {
+                !is_host_char(bytes[end])
+            };
 
         if before_ok && after_ok {
             out.push_str(&text[search..pos]);
@@ -47,3 +64,99 @@ pub(crate) fn rewrite_bare_host_at_boundaries(
     out.push_str(&text[search..]);
     Some(out)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const ORIGIN_HOST: &str = "origin.example.com";
+    const REQUEST_HOST: &str = "proxy.example.com";
+
+    fn rewrite(text: &str) -> Option<String> {
+        rewrite_bare_host_at_boundaries(text, ORIGIN_HOST, REQUEST_HOST)
+    }
+
+    #[test]
+    fn rewrites_exact_host() {
+        assert_eq!(
+            rewrite(ORIGIN_HOST),
+            Some(REQUEST_HOST.to_string()),
+            "should rewrite a host that spans the whole input"
+        );
+    }
+
+    #[test]
+    fn rewrites_valid_boundary_separators() {
+        let input = r#"("origin.example.com"), origin.example.com/path origin.example.com?x=1 origin.example.com#frag"#;
+        let expected = r#"("proxy.example.com"), proxy.example.com/path proxy.example.com?x=1 proxy.example.com#frag"#;
+
+        assert_eq!(
+            rewrite(input),
+            Some(expected.to_string()),
+            "should rewrite hosts followed by punctuation and URL separators"
+        );
+    }
+
+    #[test]
+    fn rewrites_multiple_occurrences() {
+        assert_eq!(
+            rewrite("origin.example.com origin.example.com/news origin.example.com?x=1"),
+            Some("proxy.example.com proxy.example.com/news proxy.example.com?x=1".to_string()),
+            "should rewrite every standalone occurrence"
+        );
+    }
+
+    #[test]
+    fn returns_none_for_empty_input_or_missing_origin() {
+        assert_eq!(rewrite(""), None, "should ignore empty input");
+        assert_eq!(
+            rewrite("other.example.com/news"),
+            None,
+            "should ignore input without the origin host"
+        );
+        assert_eq!(
+            rewrite_bare_host_at_boundaries("origin.example.com", "", REQUEST_HOST),
+            None,
+            "should ignore an empty origin host"
+        );
+        assert_eq!(
+            rewrite_bare_host_at_boundaries("origin.example.com", ORIGIN_HOST, ""),
+            None,
+            "should ignore an empty request host"
+        );
+    }
+
+    #[test]
+    fn does_not_rewrite_larger_hostname_tokens() {
+        let input = "cdn.origin.example.com notorigin.example.com origin.example.com.evil origin.example.com-extra origin.example.comextra";
+
+        assert_eq!(
+            rewrite(input),
+            None,
+            "should not rewrite subdomains, embedded words, or larger hostname tokens"
+        );
+    }
+
+    #[test]
+    fn rewrites_host_with_valid_numeric_port() {
+        let input = "origin.example.com:8443/path origin.example.com:9443?x=1 origin.example.com:443#frag origin.example.com:8080";
+        let expected = "proxy.example.com:8443/path proxy.example.com:9443?x=1 proxy.example.com:443#frag proxy.example.com:8080";
+
+        assert_eq!(
+            rewrite(input),
+            Some(expected.to_string()),
+            "should rewrite a standalone host while preserving a numeric port"
+        );
+    }
+
+    #[test]
+    fn does_not_rewrite_invalid_port_like_suffixes() {
+        let input = "origin.example.com:not-a-port origin.example.com:8443evil origin.example.com:8443.evil origin.example.com:";
+
+        assert_eq!(
+            rewrite(input),
+            None,
+            "should not treat arbitrary colon suffixes as host boundaries"
+        );
+    }
+}