diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 4dde7577..ddd4125c 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -13,8 +13,8 @@ jobs:
     - name: Set up Elixir
       uses: erlef/setup-beam@v1
       with:
-        elixir-version: '1.13'
-        otp-version: '24.3'
+        version-file: .tool-versions
+        version-type: strict
     - name: Restore dependencies cache
       uses: actions/cache@v4
       with:
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index fede8547..6582ff82 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -9,11 +9,11 @@ jobs:
     strategy:
       matrix:
         elixir:
-          - 1.14
-          - 1.13
+          - 1.16
+          - 1.15
         otp:
+          - 26.2
           - 25.3
-          - 24.3
     steps:
     - uses: actions/checkout@v4
     - name: Set up Elixir
@@ -83,8 +83,8 @@ jobs:
     - name: Set up Elixir
       uses: erlef/setup-beam@v1
       with:
-        elixir-version: '1.13'
-        otp-version: '24.3'
+        elixir-version: '1.15'
+        otp-version: '26.1'
         version-type: strict
     - name: Restore dependencies cache
       uses: actions/cache@v4
diff --git a/.tool-versions b/.tool-versions
new file mode 100644
index 00000000..fae1b1a2
--- /dev/null
+++ b/.tool-versions
@@ -0,0 +1,2 @@
+elixir 1.16.2
+erlang 26.2.3
diff --git a/lib/tesla/adapter/hackney.ex b/lib/tesla/adapter/hackney.ex
index e5965857..3d080787 100644
--- a/lib/tesla/adapter/hackney.ex
+++ b/lib/tesla/adapter/hackney.ex
@@ -72,7 +72,7 @@ if Code.ensure_loaded?(:hackney) do
     end
 
     defp request(method, url, headers, body, opts) do
-      handle(:hackney.request(method, url, headers, body || '', opts), opts)
+      handle(:hackney.request(method, url, headers, body || ~c"", opts), opts)
     end
 
     defp request_stream(method, url, headers, body, opts) do
diff --git a/lib/tesla/adapter/httpc.ex b/lib/tesla/adapter/httpc.ex
index 5d79a6e1..ebaff440 100644
--- a/lib/tesla/adapter/httpc.ex
+++ b/lib/tesla/adapter/httpc.ex
@@ -80,8 +80,8 @@ defmodule Tesla.Adapter.Httpc do
     headers = for {key, value} <- headers, do: {to_charlist(key), to_charlist(value)}
 
     {content_type, headers} =
-      case List.keytake(headers, 'content-type', 0) do
-        nil -> {'text/plain', headers}
+      case List.keytake(headers, ~c"content-type", 0) do
+        nil -> {~c"text/plain", headers}
         {{_, ct}, headers} -> {ct, headers}
       end
 
diff --git a/test/tesla/middleware/timeout_test.exs b/test/tesla/middleware/timeout_test.exs
index 760ff573..3a51a76e 100644
--- a/test/tesla/middleware/timeout_test.exs
+++ b/test/tesla/middleware/timeout_test.exs
@@ -115,7 +115,7 @@ defmodule Tesla.Middleware.TimeoutTest do
           [{last_module, _, _, file_info} | _] = __STACKTRACE__
 
           assert Tesla.Middleware.TimeoutTest.Client == last_module
-          assert file_info[:file] == 'lib/tesla/builder.ex'
+          assert file_info[:file] == ~c"lib/tesla/builder.ex"
           assert file_info[:line] == 23
       else
         _ ->
@@ -131,7 +131,7 @@ defmodule Tesla.Middleware.TimeoutTest do
           [_, {timeout_module, _, _, module_file_info} | _] = __STACKTRACE__
 
           assert Tesla.Middleware.Timeout == timeout_module
-          assert module_file_info == [file: 'lib/tesla/middleware/timeout.ex', line: 59]
+          assert module_file_info == [file: ~c"lib/tesla/middleware/timeout.ex", line: 59]
       else
         _ ->
           flunk("Expected exception to be thrown")