diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 4dedeae..fe26bee 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "2.5.0"
+  ".": "2.5.1"
 }
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 647b86a..44739ee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 2.5.1 (2026-02-03)
+
+Full Changelog: [v2.5.0...v2.5.1](https://github.com/moderation-api/sdk-ruby/compare/v2.5.0...v2.5.1)
+
+### Bug Fixes
+
+* **client:** always add content-length to post body, even when empty ([22201f0](https://github.com/moderation-api/sdk-ruby/commit/22201f0900c1c285c0900dec155b5e0718ccc035))
+
 ## 2.5.0 (2026-01-28)
 
 Full Changelog: [v2.4.0...v2.5.0](https://github.com/moderation-api/sdk-ruby/compare/v2.4.0...v2.5.0)
diff --git a/Gemfile.lock b/Gemfile.lock
index 1f160e6..cbe877c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -11,7 +11,7 @@ GIT
 PATH
   remote: .
   specs:
-    moderation_api (2.5.0)
+    moderation_api (2.5.1)
       cgi
       connection_pool
 
diff --git a/README.md b/README.md
index 49ea1a0..20dc2ef 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ To use this gem, install via Bundler by adding the following to your application
 <!-- x-release-please-start-version -->
 
 ```ruby
-gem "moderation_api", "~> 2.5.0"
+gem "moderation_api", "~> 2.5.1"
 ```
 
 <!-- x-release-please-end -->
diff --git a/lib/moderation_api/internal/transport/pooled_net_requester.rb b/lib/moderation_api/internal/transport/pooled_net_requester.rb
index d67d6f4..fddc58f 100644
--- a/lib/moderation_api/internal/transport/pooled_net_requester.rb
+++ b/lib/moderation_api/internal/transport/pooled_net_requester.rb
@@ -75,7 +75,7 @@ def build_request(request, &blk)
 
             case body
             in nil
-              nil
+              req["content-length"] ||= 0 unless req["transfer-encoding"]
             in String
               req["content-length"] ||= body.bytesize.to_s unless req["transfer-encoding"]
               req.body_stream = ModerationAPI::Internal::Util::ReadIOAdapter.new(body, &blk)
diff --git a/lib/moderation_api/version.rb b/lib/moderation_api/version.rb
index faa0b01..ef6ebaa 100644
--- a/lib/moderation_api/version.rb
+++ b/lib/moderation_api/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module ModerationAPI
-  VERSION = "2.5.0"
+  VERSION = "2.5.1"
 end