diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ef22472f..e0b920a9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,7 +17,7 @@ jobs:
       matrix:
         include:
           # Earliest-supported Elixir/Erlang pair.
-          - elixir: "1.14"
+          - elixir: "1.15"
             otp: "24"
             PLUG_CRYPTO_2_0: "false"
 
diff --git a/lib/plug/router/utils.ex b/lib/plug/router/utils.ex
index b24a6979..ae43f125 100644
--- a/lib/plug/router/utils.ex
+++ b/lib/plug/router/utils.ex
@@ -151,7 +151,7 @@ defmodule Plug.Router.Utils do
       [{prefix_size, match_length}] when match_length == 2 ->
         suffix_size = byte_size(segment) - prefix_size - 2
 
-        <<prefix::binary-size(prefix_size), ?\\, char, suffix::binary-size(suffix_size)>> =
+        <<prefix::binary-size(^prefix_size), ?\\, char, suffix::binary-size(^suffix_size)>> =
           segment
 
         escaped_segment = [prefix <> <<char>> <> suffix | match]
@@ -159,7 +159,7 @@ defmodule Plug.Router.Utils do
 
       [{prefix_size, _}] ->
         suffix_size = byte_size(segment) - prefix_size - 1
-        <<prefix::binary-size(prefix_size), char, suffix::binary-size(suffix_size)>> = segment
+        <<prefix::binary-size(^prefix_size), char, suffix::binary-size(^suffix_size)>> = segment
         {param, suffix} = parse_suffix(suffix)
         params = [param | params]
         var = Macro.var(String.to_atom(param), context)
diff --git a/mix.exs b/mix.exs
index 90d7eff1..27c257c6 100644
--- a/mix.exs
+++ b/mix.exs
@@ -10,7 +10,7 @@ defmodule Plug.MixProject do
     [
       app: :plug,
       version: @version,
-      elixir: "~> 1.14",
+      elixir: "~> 1.15",
       deps: deps(),
       package: package(),
       description: @description,