diff --git a/client/js/upload-handler/upload.handler.controller.js b/client/js/upload-handler/upload.handler.controller.js
index 1141824a4..71aa5d44e 100644
--- a/client/js/upload-handler/upload.handler.controller.js
+++ b/client/js/upload-handler/upload.handler.controller.js
@@ -77,8 +77,8 @@ qq.UploadHandlerController = function(o, namespace) {
                     log("Problem finalizing chunks for file ID " + id + " - " + normalizedResponse.error, "error");
 
                     if (
-                        normalizedResponse.reset
-                        || (xhr && options.chunking.success.resetOnStatus.indexOf(xhr.status) >= 0)
+                        normalizedResponse.reset ||
+                        (xhr && options.chunking.success.resetOnStatus.indexOf(xhr.status) >= 0)
                     ) {
                         chunked.reset(id);
                     }
diff --git a/client/js/upload-handler/xhr.upload.handler.js b/client/js/upload-handler/xhr.upload.handler.js
index 549e65150..7ac45aa7e 100644
--- a/client/js/upload-handler/xhr.upload.handler.js
+++ b/client/js/upload-handler/xhr.upload.handler.js
@@ -12,6 +12,24 @@ qq.XhrUploadHandler = function(spec) {
         namespace = spec.options.namespace,
         proxy = spec.proxy,
         chunking = spec.options.chunking,
+        getChunkSize = function(id) {
+            var fileState = handler._getFileState(id);
+
+            if (fileState.chunkSize) {
+                return fileState.chunkSize;
+            }
+
+            else {
+                var chunkSize = chunking.partSize;
+
+                if (qq.isFunction(chunkSize)) {
+                    chunkSize = chunkSize(id, getSize(id));
+                }
+
+                fileState.chunkSize = chunkSize;
+                return chunkSize;
+            }
+        },
         resume = spec.options.resume,
         chunkFiles = chunking && spec.options.chunking.enabled && qq.supportedFeatures.chunking,
         resumeEnabled = resume && spec.options.resume.enabled && chunkFiles && qq.supportedFeatures.resume,
@@ -141,8 +159,8 @@ qq.XhrUploadHandler = function(spec) {
         },
 
         isResumable: function(id) {
-            return !!chunking && handler.isValid(id)
-                && !handler._getFileState(id).notResumable;
+            return !!chunking && handler.isValid(id) &&
+                !handler._getFileState(id).notResumable;
         },
 
         moveInProgressToRemaining: function(id, optInProgress, optRemaining) {
@@ -232,7 +250,7 @@ qq.XhrUploadHandler = function(spec) {
         },
 
         _getChunkData: function(id, chunkIndex) {
-            var chunkSize = chunking.partSize,
+            var chunkSize = getChunkSize(id),
                 fileSize = getSize(id),
                 fileOrBlob = handler.getFile(id),
                 startBytes = chunkSize * chunkIndex,
@@ -273,7 +291,7 @@ qq.XhrUploadHandler = function(spec) {
             var formatVersion = "5.0",
                 name = getName(id),
                 size = getSize(id),
-                chunkSize = chunking.partSize,
+                chunkSize = getChunkSize(id),
                 endpoint = getEndpoint(id),
                 customKeys = resume.customKeys(id),
                 localStorageId = qq.format("qq{}resume{}-{}-{}-{}-{}", namespace, formatVersion, name, size, chunkSize, endpoint);
@@ -300,7 +318,7 @@ qq.XhrUploadHandler = function(spec) {
         _getTotalChunks: function(id) {
             if (chunking) {
                 var fileSize = getSize(id),
-                    chunkSize = chunking.partSize;
+                    chunkSize = getChunkSize(id);
 
                 return Math.ceil(fileSize / chunkSize);
             }
diff --git a/client/js/uploader.basic.js b/client/js/uploader.basic.js
index 06a365c4b..4998ca2bf 100644
--- a/client/js/uploader.basic.js
+++ b/client/js/uploader.basic.js
@@ -111,7 +111,9 @@
                     totalFileSize: "qqtotalfilesize",
                     totalParts: "qqtotalparts"
                 },
-                partSize: 2000000,
+                partSize: function(id) {
+                    return 2000000;
+                },
                 // only relevant for traditional endpoints, only required when concurrent.enabled === true
                 success: {
                     endpoint: null,
diff --git a/client/js/version.js b/client/js/version.js
index e29d7823c..04aeb9ec6 100644
--- a/client/js/version.js
+++ b/client/js/version.js
@@ -1,2 +1,2 @@
 /*global qq */
-qq.version = "5.16.0-alpha.11";
+qq.version = "5.16.0-alpha.12";
diff --git a/package.json b/package.json
index 21cc7deef..849e02dea 100644
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
   "title": "Fine Uploader",
   "main": "lib/traditional.js",
   "types" : "typescript/fine-uploader.d.ts",
-  "version": "5.16.0-alpha.11",
+  "version": "5.16.0-alpha.12",
   "description": "Multiple file upload plugin with progress-bar, drag-and-drop, direct-to-S3 & Azure uploading, client-side image scaling, preview generation, form support, chunking, auto-resume, and tons of other features.",
   "keywords": [
     "amazon",