diff --git a/lib/web/fetch/response.js b/lib/web/fetch/response.js
index 182e3dc0199..acd063915cf 100644
--- a/lib/web/fetch/response.js
+++ b/lib/web/fetch/response.js
@@ -146,7 +146,7 @@ class Response {
     // 4. If body is non-null, then set bodyWithType to the result of extracting body.
     if (body != null) {
       const [extractedBody, type] = extractBody(body)
-      bodyWithType = { body: extractedBody, type }
+      bodyWithType = { body: extractedBody, type, source: body }
     }
 
     // 5. Perform initialize a response given this, init, and bodyWithType.
diff --git a/lib/web/fetch/util.js b/lib/web/fetch/util.js
index 8c73f909604..7e6afba3cf1 100644
--- a/lib/web/fetch/util.js
+++ b/lib/web/fetch/util.js
@@ -1055,6 +1055,11 @@ async function fullyReadBody (body, processBody, processBodyError) {
   //    with taskDestination.
   const errorSteps = processBodyError
 
+  if (typeof body.source === 'string') {
+    successSteps(new TextEncoder().encode(body.source))
+    return
+  }
+
   // 4. Let reader be the result of getting a reader for body’s stream.
   //    If that threw an exception, then run errorSteps with that
   //    exception and return.