diff --git a/ext/fetch/lib.rs b/ext/fetch/lib.rs
index 5a95fbd30c..f79fc33f4e 100644
--- a/ext/fetch/lib.rs
+++ b/ext/fetch/lib.rs
@@ -534,7 +534,7 @@ impl Resource for FetchResponseBodyResource {
   }
 
   fn size_hint(&self) -> (u64, Option<u64>) {
-    (0, self.size)
+    (self.size.unwrap_or(0), self.size)
   }
 
   fn close(self: Rc<Self>) {