diff --git a/components/script/dom/globalscope.rs b/components/script/dom/globalscope.rs
index ac2497da004..9a3829f4d0e 100644
--- a/components/script/dom/globalscope.rs
+++ b/components/script/dom/globalscope.rs
@@ -1838,13 +1838,16 @@ impl GlobalScope {
             };
             match parent {
                 Some((parent_id, rel_pos)) => {
-                    let parent_file_id = {
-                        let parent_info = blobs_map
-                            .get_mut(&parent_id)
-                            .expect("Parent of blob whose url is requested is unknown.");
-                        self.promote(parent_info, /* set_valid is */ false)
+                    let parent_info = blobs_map
+                        .get_mut(&parent_id)
+                        .expect("Parent of blob whose url is requested is unknown.");
+                    let parent_file_id = self.promote(parent_info, /* set_valid is */ false);
+                    let parent_size = match parent_info.blob_impl.blob_data() {
+                        BlobData::File(ref f) => f.get_size(),
+                        BlobData::Memory(ref v) => v.len() as u64,
+                        BlobData::Sliced(_, _) => panic!("Blob ancestry should be only one level."),
                     };
-                    let parent_size = self.get_blob_size(&parent_id);
+                    let parent_size = rel_pos.to_abs_range(parent_size as usize).len() as u64;
                     let blob_info = blobs_map
                         .get_mut(blob_id)
                         .expect("Blob whose url is requested is unknown.");
diff --git a/tests/wpt/metadata/fetch/api/basic/scheme-blob.sub.any.js.ini b/tests/wpt/metadata/fetch/api/basic/scheme-blob.sub.any.js.ini
index 04f3b0fe381..dcb842c4c4c 100644
--- a/tests/wpt/metadata/fetch/api/basic/scheme-blob.sub.any.js.ini
+++ b/tests/wpt/metadata/fetch/api/basic/scheme-blob.sub.any.js.ini
@@ -1,5 +1,44 @@
 [scheme-blob.sub.any.html]
-  expected: CRASH
+  [Fetching URL.createObjectURL(empty_blob) is OK]
+    expected: FAIL
+
+  [Fetching URL.createObjectURL(empty_type_blob) is OK]
+    expected: FAIL
+
+  [Blob content is not sniffed for a content type [image/png\]]
+    expected: FAIL
+
+  [Blob content is not sniffed for a content type [text/xml\]]
+    expected: FAIL
+
+  [Set content type to the empty string for slice with invalid content type]
+    expected: FAIL
+
+  [Set content type to the empty string for slice with no content type ]
+    expected: FAIL
+
+  [Blob.slice should not sniff the content for a content type]
+    expected: FAIL
+
 
 [scheme-blob.sub.any.worker.html]
-  expected: CRASH
+  [Fetching URL.createObjectURL(empty_blob) is OK]
+    expected: FAIL
+
+  [Fetching URL.createObjectURL(empty_type_blob) is OK]
+    expected: FAIL
+
+  [Blob content is not sniffed for a content type [image/png\]]
+    expected: FAIL
+
+  [Blob content is not sniffed for a content type [text/xml\]]
+    expected: FAIL
+
+  [Set content type to the empty string for slice with invalid content type]
+    expected: FAIL
+
+  [Set content type to the empty string for slice with no content type ]
+    expected: FAIL
+
+  [Blob.slice should not sniff the content for a content type]
+    expected: FAIL