diff --git a/Sources/Storage/StorageFileApi.swift b/Sources/Storage/StorageFileApi.swift
index 7e5a6a874..ba9d14d7a 100644
--- a/Sources/Storage/StorageFileApi.swift
+++ b/Sources/Storage/StorageFileApi.swift
@@ -955,7 +955,7 @@ public class StorageFileApi: StorageApi, @unchecked Sendable {
     file: FileUpload,
     options: FileOptions?
   ) async throws -> SignedURLUploadResponse {
-    let options = options ?? defaultFileOptions
+    let options = options ?? FileOptions()
     var headers = options.headers.map { HTTPFields($0) } ?? HTTPFields()
 
     headers[.xUpsert] = "\(options.upsert)"
diff --git a/Tests/StorageTests/StorageFileAPITests.swift b/Tests/StorageTests/StorageFileAPITests.swift
index 0be414046..b2ce4eaaf 100644
--- a/Tests/StorageTests/StorageFileAPITests.swift
+++ b/Tests/StorageTests/StorageFileAPITests.swift
@@ -45,6 +45,37 @@ extension StorageMockerTests {
       )
     }
 
+    /// A client whose transport records the request body, for asserting the emitted multipart
+    /// headers.
+    private func makeBodyCapturingSUT(body: LockIsolated<Data>) -> SupabaseStorageClient {
+      let respond: @Sendable (URLRequest) -> (Data, URLResponse) = { request in
+        (
+          Data(#"{"Key":"bucket/\#(request.url!.lastPathComponent)"}"#.utf8),
+          HTTPURLResponse(
+            url: request.url!, statusCode: 200, httpVersion: nil, headerFields: nil
+          )!
+        )
+      }
+
+      return SupabaseStorageClient(
+        configuration: StorageClientConfiguration(
+          url: url,
+          headers: [:],
+          session: StorageHTTPSession(
+            fetch: { request in
+              body.setValue(request.httpBody ?? Data())
+              return respond(request)
+            },
+            upload: { request, data in
+              body.setValue(data)
+              return respond(request)
+            }
+          ),
+          logger: nil
+        )
+      )
+    }
+
     @Test
     func listFiles() async throws {
       let storage = makeSUT()
@@ -1410,7 +1441,7 @@ extension StorageMockerTests {
         curl \
         	--request PUT \
         	--header "Cache-Control: max-age=3600" \
-        	--header "Content-Length: 297" \
+        	--header "Content-Length: 283" \
         	--header "Content-Type: multipart/form-data; boundary=alamofire.boundary.e56f43407f772505" \
         	--header "X-Client-Info: storage-swift/0.0.0" \
         	--header "apikey: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJzdXBhYmFzZS1kZW1vIiwicm9sZSI6ImFub24iLCJleHAiOjE5ODM4MTI5OTZ9.CRXP1A7WOeoJeXxjNni43kdQwgnWNReilDMblYTn_I0" \
@@ -1421,7 +1452,7 @@ extension StorageMockerTests {
         3600\#r
         --alamofire.boundary.e56f43407f772505\#r
         Content-Disposition: form-data; name=\"\"; filename=\"file.txt\"\#r
-        Content-Type: text/plain;charset=UTF-8\#r
+        Content-Type: text/plain\#r
         \#r
         hello world\#r
         --alamofire.boundary.e56f43407f772505--\#r
@@ -1438,6 +1469,38 @@ extension StorageMockerTests {
       #expect(response.fullPath == "bucket/file.txt")
     }
 
+    @Test
+    func uploadToSignedURLDerivesContentTypeFromPathExtensionWhenOptionsOmitted() async throws {
+      let body = LockIsolated(Data())
+      let storage = makeBodyCapturingSUT(body: body)
+
+      _ = try await storage.from("bucket")
+        .uploadToSignedURL(
+          "cat.png",
+          token: "abc.def.ghi",
+          data: Data("not-really-a-png".utf8)
+        )
+
+      #expect(body.value.containsBytes(of: "Content-Type: image/png"))
+      #expect(!body.value.containsBytes(of: "text/plain"))
+    }
+
+    @Test
+    func uploadToSignedURLFromFileURLDerivesContentTypeWhenOptionsOmitted() async throws {
+      let body = LockIsolated(Data())
+      let storage = makeBodyCapturingSUT(body: body)
+
+      _ = try await storage.from("bucket")
+        .uploadToSignedURL(
+          "cat.jpg",
+          token: "abc.def.ghi",
+          fileURL: Bundle.module.url(forResource: "sadcat", withExtension: "jpg")!
+        )
+
+      #expect(body.value.containsBytes(of: "Content-Type: image/jpeg"))
+      #expect(!body.value.containsBytes(of: "text/plain"))
+    }
+
     @Test
     func uploadToSignedURL_fromFileURL() async throws {
       let storage = makeSUT()
@@ -1603,3 +1666,10 @@ extension StorageMockerTests {
     }
   }
 }
+
+extension Data {
+  /// Whether the raw bytes contain `string`, for bodies that are not valid UTF-8 as a whole.
+  fileprivate func containsBytes(of string: String) -> Bool {
+    range(of: Data(string.utf8)) != nil
+  }
+}