diff --git a/src/main/java/com/convertapi/client/ConvertApi.java b/src/main/java/com/convertapi/client/ConvertApi.java
index 2393292..f85bc20 100644
--- a/src/main/java/com/convertapi/client/ConvertApi.java
+++ b/src/main/java/com/convertapi/client/ConvertApi.java
@@ -71,6 +71,7 @@ public static CompletableFuture<ConversionResult> convert(String fromFormat, Str
             Request request = Http.getRequestBuilder()
                 .url(url)
                 .addHeader("Accept", "application/json")
+                .addHeader("Content-Type", "multipart/form-data")
                 .post(multipartBuilder.build())
                 .build();
 
diff --git a/src/main/java/com/convertapi/client/Http.java b/src/main/java/com/convertapi/client/Http.java
index 1d86a34..bca3562 100644
--- a/src/main/java/com/convertapi/client/Http.java
+++ b/src/main/java/com/convertapi/client/Http.java
@@ -66,6 +66,7 @@ static CompletableFuture<Void> requestDelete(String url) {
             } catch (IOException e) {
                 throw new RuntimeException(e);
             }
+            return null;
         });
     }