diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index 2fa7e89952..167bbdead6 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -403,7 +403,8 @@ Handle<Value> Buffer::Copy(const Arguments &args) {
   size_t target_length = Buffer::Length(target);
   size_t target_start = args[1]->Uint32Value();
   size_t source_start = args[2]->Uint32Value();
-  size_t source_end = args[3]->Uint32Value();
+  size_t source_end = args[3]->IsUint32() ? args[3]->Uint32Value()
+                                          : source->length_;
 
   if (source_end < source_start) {
     return ThrowRangeError("sourceEnd < sourceStart");