diff --git a/index.js b/index.js
index a6954ce..65331aa 100644
--- a/index.js
+++ b/index.js
@@ -138,7 +138,7 @@ class Blob {
 			} else {
 				const chunk = part.slice(relativeStart, Math.min(size, relativeEnd));
 				blobParts.push(chunk);
-				added += size;
+				added += ArrayBuffer.isView(chunk) ? chunk.byteLength : chunk.size;
 				relativeStart = 0; // All next sequental parts should start at 0
 
 				// don't add the overflow to new blobParts
diff --git a/test.js b/test.js
index 52fdb72..ae73beb 100644
--- a/test.js
+++ b/test.js
@@ -114,6 +114,12 @@ test('Blob slice(0, -1)', async t => {
 	t.is(await blob.text(), 'abcdefg');
 });
 
+test('Blob(["hello ", "world"]).slice(5)', async t => {
+	const parts = ['hello ', 'world'];
+	const blob = new Blob(parts);
+	t.is(await blob.slice(5).text(), ' world');
+});
+
 test('throw away unwanted parts', async t => {
 	const blob = new Blob(['a', 'b', 'c']).slice(1, 2);
 	t.is(await blob.text(), 'b');