diff --git a/src/resource-archive/index.test.ts b/src/resource-archive/index.test.ts
index 8a4213c6..8b99760b 100644
--- a/src/resource-archive/index.test.ts
+++ b/src/resource-archive/index.test.ts
@@ -129,7 +129,7 @@ describe('new', () => {
         statusCode: 200,
         statusText: 'OK',
         body: Buffer.from(imgPng, 'base64'),
-        contentType: undefined,
+        contentType: 'image/png',
       },
     });
   });
@@ -155,7 +155,7 @@ describe('new', () => {
         statusCode: 200,
         statusText: 'OK',
         body: Buffer.from(imgPng, 'base64'),
-        contentType: undefined,
+        contentType: 'image/png',
       },
     });
   });
@@ -195,7 +195,7 @@ describe('new', () => {
         statusCode: 200,
         statusText: 'OK',
         body: Buffer.from(imgPng, 'base64'),
-        contentType: undefined,
+        contentType: 'image/png',
       },
       // includes cross-origin images
       'https://i-ama.fake/external/domain/image.png': {
diff --git a/src/resource-archive/index.ts b/src/resource-archive/index.ts
index d03ff3cd..a6cf9975 100644
--- a/src/resource-archive/index.ts
+++ b/src/resource-archive/index.ts
@@ -184,7 +184,7 @@ class Watcher {
 
       // If the Content-Type header is present, let's capture it.
       const contentTypeHeader: Protocol.Fetch.HeaderEntry = responseHeaders.find(
-        ({ name }) => name === 'Content-Type'
+        ({ name }) => name.toLowerCase() === 'content-type'
       );
 
       // No need to capture the response of the top level page request