diff --git a/lib/diff.js b/lib/diff.js
index 34c279047..b397ecd2b 100644
--- a/lib/diff.js
+++ b/lib/diff.js
@@ -72,7 +72,7 @@ Diff.blobToBuffer= function(
   var bufferLength;
   if (buffer instanceof Buffer) {
     bufferText = buffer.toString("utf8");
-    bufferLength = buffer.length;
+    bufferLength = Buffer.byteLength(buffer, "utf8");
   } else {
     bufferText = buffer;
     bufferLength = !buffer ? 0 : Buffer.byteLength(buffer, "utf8");
@@ -84,7 +84,7 @@ Diff.blobToBuffer= function(
     this,
     old_blob,
     old_as_path,
-    buffer,
+    bufferText,
     bufferLength,
     buffer_as_path,
     opts,