diff --git a/src/at/nsid.gleam b/src/at/nsid.gleam
index eb5cefb..8796076 100644
--- a/src/at/nsid.gleam
+++ b/src/at/nsid.gleam
@@ -1,5 +1,6 @@
 // IMPORTS ---------------------------------------------------------------------
 
+import at/internal/ascii
 import gleam/dynamic/decode.{type Decoder}
 import gleam/json.{type Json}
 import gleam/list
@@ -55,7 +56,8 @@ pub opaque type Nsid {
 
 // CONSTANTS -------------------------------------------------------------------
 
-const zero = Nsid(authority: [], name: "")
+@internal
+pub const zero = Nsid(authority: [], name: "")
 
 // CONSTRUCTORS ----------------------------------------------------------------
 
@@ -74,7 +76,7 @@ const zero = Nsid(authority: [], name: "")
 /// - `"app.bsky.feed.post"`
 /// 
 pub fn from_string(input: String) -> Result(Nsid, Nil) {
-  do_from_string(input, input, 0, 0, [], 0, 0)
+  do_from_string(input, input, 0, 0, [], 0, 0, False)
 }
 
 fn do_from_string(
@@ -87,6 +89,8 @@ fn do_from_string(
   authority_segments: List(String),
   authority_count: Int,
   authority_length: Int,
+  // 
+  segment_has_hyphen: Bool,
 ) -> Result(Nsid, Nil) {
   case remaining {
     // An NSID must have at least three segments, so at least two authority
@@ -111,9 +115,12 @@ fn do_from_string(
       || slice_length > 63
     -> Error(Nil)
 
+    // The name segment must not contain a hyphen.
+    "" if segment_has_hyphen -> Error(Nil)
+
     "" ->
       // The name segment must not start with a digit.
-      case string.slice(input, slice_offset, slice_length) {
+      case ascii.slice(input, slice_offset, slice_length) {
         "0" <> _
         | "1" <> _
         | "2" <> _
@@ -125,13 +132,7 @@ fn do_from_string(
         | "8" <> _
         | "9" <> _ -> Error(Nil)
 
-        name ->
-          // The name segment must not contain a hyphen.
-          case string.contains(name, "-") {
-            True -> Error(Nil)
-            False ->
-              Ok(Nsid(authority: list.reverse(authority_segments), name:))
-          }
+        name -> Ok(Nsid(authority: list.reverse(authority_segments), name:))
       }
 
     // Each segment must be at least 1 character long and no more than 63 characters.
@@ -140,7 +141,7 @@ fn do_from_string(
     "." <> remaining if authority_length == 0 -> {
       let slice =
         input
-        |> string.slice(slice_offset, slice_length)
+        |> ascii.slice(slice_offset, slice_length)
         |> string.lowercase
       let slice_length = slice_length + 1
 
@@ -152,13 +153,14 @@ fn do_from_string(
         [slice],
         1,
         slice_length,
+        False,
       )
     }
 
     "." <> remaining -> {
       let slice =
         input
-        |> string.slice(slice_offset, slice_length)
+        |> ascii.slice(slice_offset, slice_length)
         |> string.lowercase
       let slice_length = slice_length + 1
 
@@ -170,6 +172,7 @@ fn do_from_string(
         [slice, ..authority_segments],
         authority_count + 1,
         authority_length + slice_length,
+        False,
       )
     }
 
@@ -209,8 +212,8 @@ fn do_from_string(
     | "d" <> remaining
     | "e" <> remaining
     | "f" <> remaining
-    | "h" <> remaining
     | "g" <> remaining
+    | "h" <> remaining
     | "i" <> remaining
     | "j" <> remaining
     | "k" <> remaining
@@ -252,11 +255,27 @@ fn do_from_string(
     | "T" <> remaining
     | "U" <> remaining
     | "V" <> remaining
-    | "Y" <> remaining
     | "W" <> remaining
     | "X" <> remaining
-    | "Z" <> remaining
-    | "-" <> remaining ->
+    | "Y" <> remaining
+    | "Z" <> remaining ->
+      do_from_string(
+        input,
+        remaining,
+        slice_offset,
+        slice_length + 1,
+        authority_segments,
+        authority_count,
+        authority_length,
+        segment_has_hyphen,
+      )
+
+    // A hyphen is valid within a segment (leading/trailing hyphens in an
+    // authority segment are rejected above); we don't yet know whether this
+    // segment will turn out to be an authority segment (hyphens allowed) or
+    // the final name segment (hyphens disallowed), so record that we've seen
+    // one and check again once we reach the end of the current segment.
+    "-" <> remaining ->
       do_from_string(
         input,
         remaining,
@@ -265,6 +284,7 @@ fn do_from_string(
         authority_segments,
         authority_count,
         authority_length,
+        True,
       )
 
     _ -> Error(Nil)