diff --git a/lib/browser/managed-upload.js b/lib/browser/managed-upload.js
index 147509238..002a40447 100644
--- a/lib/browser/managed-upload.js
+++ b/lib/browser/managed-upload.js
@@ -301,16 +301,16 @@ proto._createStream = function _createStream(file, start, end) {
 
 proto._getPartSize = function _getPartSize(fileSize, partSize) {
   const maxNumParts = 10 * 1000;
-  const defaultPartSize = 1024 * 1024;
+  const defaultPartSize = 1 * 1024 * 1024;
 
-  if (!partSize) {
-    return defaultPartSize;
-  }
+  if (!partSize) partSize = defaultPartSize;
+  const safeSize = Math.ceil(fileSize / maxNumParts);
 
-  return Math.max(
-    Math.ceil(fileSize / maxNumParts),
-    partSize
-  );
+  if (partSize < safeSize) {
+    partSize = safeSize;
+    console.warn(`partSize has been set to ${partSize}, because the partSize you provided causes partNumber to be greater than 10,000`);
+  }
+  return partSize;
 };
 
 proto._divideParts = function _divideParts(fileSize, partSize) {
diff --git a/lib/managed-upload.js b/lib/managed-upload.js
index 6feac50ec..2a4dd133a 100644
--- a/lib/managed-upload.js
+++ b/lib/managed-upload.js
@@ -295,14 +295,14 @@ proto._getPartSize = function _getPartSize(fileSize, partSize) {
   const maxNumParts = 10 * 1000;
   const defaultPartSize = 1 * 1024 * 1024;
 
-  if (!partSize) {
-    return defaultPartSize;
-  }
+  if (!partSize) partSize = defaultPartSize;
+  const safeSize = Math.ceil(fileSize / maxNumParts);
 
-  return Math.max(
-    Math.ceil(fileSize / maxNumParts),
-    partSize
-  );
+  if (partSize < safeSize) {
+    partSize = safeSize;
+    console.warn(`partSize has been set to ${partSize}, because the partSize you provided causes partNumber to be greater than 10,000`);
+  }
+  return partSize;
 };
 
 proto._divideParts = function _divideParts(fileSize, partSize) {