diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 0815771e..f406ff13 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "0.1.0-alpha.56"
+  ".": "0.1.0-alpha.57"
 }
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba27f311..450b7df7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.1.0-alpha.57 (2025-02-10)
+
+Full Changelog: [v0.1.0-alpha.56...v0.1.0-alpha.57](https://github.com/openai/openai-go/compare/v0.1.0-alpha.56...v0.1.0-alpha.57)
+
+### Bug Fixes
+
+* do not call path.Base on ContentType ([#225](https://github.com/openai/openai-go/issues/225)) ([7dda9a8](https://github.com/openai/openai-go/commit/7dda9a8792c5d0725614d8867d42db45cb408a91))
+
 ## 0.1.0-alpha.56 (2025-02-07)
 
 Full Changelog: [v0.1.0-alpha.55...v0.1.0-alpha.56](https://github.com/openai/openai-go/compare/v0.1.0-alpha.55...v0.1.0-alpha.56)
diff --git a/README.md b/README.md
index fdfc5049..3c849ce6 100644
--- a/README.md
+++ b/README.md
@@ -25,7 +25,7 @@ Or to pin the version:
 <!-- x-release-please-start-version -->
 
 ```sh
-go get -u 'github.com/openai/openai-go@v0.1.0-alpha.56'
+go get -u 'github.com/openai/openai-go@v0.1.0-alpha.57'
 ```
 
 <!-- x-release-please-end -->
diff --git a/internal/apiform/encoder.go b/internal/apiform/encoder.go
index 58905eab..555330ae 100644
--- a/internal/apiform/encoder.go
+++ b/internal/apiform/encoder.go
@@ -319,7 +319,7 @@ func (e *encoder) newReaderTypeEncoder() encoderFunc {
 			filename = path.Base(named.Name())
 		}
 		if typed, ok := reader.(interface{ ContentType() string }); ok {
-			contentType = path.Base(typed.ContentType())
+			contentType = typed.ContentType()
 		}
 
 		// Below is taken almost 1-for-1 from [multipart.CreateFormFile]
diff --git a/internal/version.go b/internal/version.go
index f0581560..08651e1d 100644
--- a/internal/version.go
+++ b/internal/version.go
@@ -2,4 +2,4 @@
 
 package internal
 
-const PackageVersion = "0.1.0-alpha.56" // x-release-please-version
+const PackageVersion = "0.1.0-alpha.57" // x-release-please-version