diff --git a/lib/http-api.js b/lib/http-api.js
index 987caafd3..9468d8520 100644
--- a/lib/http-api.js
+++ b/lib/http-api.js
@@ -205,6 +205,9 @@ module.exports.MatrixHttpApi.prototype = {
             url += "&filename=" + encodeURIComponent(file.name);
 
             xhr.open("POST", url);
+            if (file.type) {
+                xhr.setRequestHeader("Content-Type", file.type);
+            }
             xhr.send(file);
         } else {
             var queryParams = {