diff --git a/core/manipulate-dom.js b/core/manipulate-dom.js
index b8b475be..ec44e1a6 100644
--- a/core/manipulate-dom.js
+++ b/core/manipulate-dom.js
@@ -34,90 +34,91 @@ manipulateDOM._removeCrossOriginAndIntegrityAttr = function (details) {
         console.warn('[ LocalCDN ] browser.webRequest.filterResponseData not supported by your browser.');
         return;
     }
+    if (details.statusCode === 200) {
+        let initiatorDomain, listedToManipulateDOM, negateHtmlFilter, filtering, header;
 
-    let initiatorDomain, listedToManipulateDOM, negateHtmlFilter, filtering, header;
+        initiatorDomain = helpers.extractDomainFromUrl(details.url, true) || Address.EXAMPLE;
+        listedToManipulateDOM = stateManager._domainIsListed(initiatorDomain, 'manipulate-dom');
+        negateHtmlFilter = stateManager.getInvertOption;
 
-    initiatorDomain = helpers.extractDomainFromUrl(details.url, true) || Address.EXAMPLE;
-    listedToManipulateDOM = stateManager._domainIsListed(initiatorDomain, 'manipulate-dom');
-    negateHtmlFilter = stateManager.getInvertOption;
-
-    if ((negateHtmlFilter || listedToManipulateDOM) && !(negateHtmlFilter && listedToManipulateDOM)) {
-        filtering = true;
-    } else {
-        filtering = false;
-    }
-
-    // by Jaap (https://gitlab.com/Jaaap)
-    header = details.responseHeaders.find((h) => h.name.toLowerCase() === 'content-type');
-
-    if (header && filtering) {
-
-        let mimeType, isAllowlisted;
-
-        mimeType = header.value.replace(/;.*/, '').toLowerCase();
-        isAllowlisted = stateManager._domainIsListed(initiatorDomain);
-
-        if (!isAllowlisted && mimeType === 'text/html') {
-
-            let asciiDecoder, decoder, encoder, charset, isFirstData, filter, data;
-
-            charset = (/charset\s*=/).test(header.value) && header.value.replace(/^.*?charset\s*=\s*/, '').replace(/["']?/g, '');
-
-            // Check if charset is supported by TextDecoder()
-            if (/charset\s*=/.test(header.value) && !EncodingTypes[charset.toString().toLowerCase()]) {
-                console.error(`[ LocalCDN ] Unsupported charset: ${charset}`);
-                return;
-            }
-
-            asciiDecoder = new TextDecoder('ASCII');
-            encoder = new TextEncoder();
-            isFirstData = true;
-            filter = browser.webRequest.filterResponseData(details.requestId);
-            data = [];
-
-            header.value = 'text/html; charset=UTF-8';
-
-            // NOTE: should work if 'script' string is divided into two chunks
-            filter.ondata = (evt) => {
-                if (isFirstData) {
-                    if (!charset) {
-                        // content-type has no charset declared
-                        let htmlHead, charsetMatch;
-
-                        htmlHead = asciiDecoder.decode(evt.data, {'stream': false});
-                        // eslint-disable-next-line no-useless-escape
-                        charsetMatch = htmlHead.match(/<meta.*charset=["']?([^>"'\/]+)["'].*[>\/]/i);
-
-                        charset = charsetMatch ? charsetMatch[1] : 'UTF-8';
-                    }
-                    decoder = new TextDecoder(charset);
-                }
-                isFirstData = false;
-
-                data.push(evt.data);
-            };
-
-            filter.onstop = () => {
-                let str = '';
-                for (let buffer of data) {
-                    str += decoder.decode(buffer, {'stream': true});
-                }
-                str += decoder.decode(); // end-of-stream
-
-                // remove crossorigin and integrity attributes
-                str = str.replace(/<(link|script)[^>]+>/ig, (m) => {
-                    // eslint-disable-next-line no-use-before-define
-                    if (cdnDomainsRE.test(m)) {
-                        return m.replace(/\s+(integrity|crossorigin)(="[^"]*"|='[^']*'|=[^"'`=>\s]+|)/ig, '');
-                    }
-                    return m;
-                });
-                filter.write(encoder.encode(str));
-                filter.close();
-            };
+        if ((negateHtmlFilter || listedToManipulateDOM) && !(negateHtmlFilter && listedToManipulateDOM)) {
+            filtering = true;
+        } else {
+            filtering = false;
         }
-        return {'responseHeaders': details.responseHeaders};
 
+        // by Jaap (https://gitlab.com/Jaaap)
+        header = details.responseHeaders.find((h) => h.name.toLowerCase() === 'content-type');
+
+        if (header && filtering) {
+
+            let mimeType, isAllowlisted;
+
+            mimeType = header.value.replace(/;.*/, '').toLowerCase();
+            isAllowlisted = stateManager._domainIsListed(initiatorDomain);
+
+            if (!isAllowlisted && mimeType === 'text/html') {
+
+                let asciiDecoder, decoder, encoder, charset, isFirstData, filter, data;
+
+                charset = (/charset\s*=/).test(header.value) && header.value.replace(/^.*?charset\s*=\s*/, '').replace(/["']?/g, '');
+
+                // Check if charset is supported by TextDecoder()
+                if (/charset\s*=/.test(header.value) && !EncodingTypes[charset.toString().toLowerCase()]) {
+                    console.error(`[ LocalCDN ] Unsupported charset: ${charset}`);
+                    return;
+                }
+
+                asciiDecoder = new TextDecoder('ASCII');
+                encoder = new TextEncoder();
+                isFirstData = true;
+                filter = browser.webRequest.filterResponseData(details.requestId);
+                data = [];
+
+                header.value = 'text/html; charset=UTF-8';
+
+                // NOTE: should work if 'script' string is divided into two chunks
+                filter.ondata = (evt) => {
+                    if (isFirstData) {
+                        if (!charset) {
+                            // content-type has no charset declared
+                            let htmlHead, charsetMatch;
+
+                            htmlHead = asciiDecoder.decode(evt.data, {'stream': false});
+                            // eslint-disable-next-line no-useless-escape
+                            charsetMatch = htmlHead.match(/<meta.*charset=["']?([^>"'\/]+)["'].*[>\/]/i);
+
+                            charset = charsetMatch ? charsetMatch[1] : 'UTF-8';
+                        }
+                        decoder = new TextDecoder(charset);
+                    }
+                    isFirstData = false;
+
+                    data.push(evt.data);
+                };
+
+                filter.onstop = () => {
+                    let str = '';
+                    for (let buffer of data) {
+                        str += decoder.decode(buffer, {'stream': true});
+                    }
+                    str += decoder.decode(); // end-of-stream
+
+                    // remove crossorigin and integrity attributes
+                    str = str.replace(/<(link|script)[^>]+>/ig, (m) => {
+                        // eslint-disable-next-line no-use-before-define
+                        if (cdnDomainsRE.test(m)) {
+                            return m.replace(/\s+(integrity|crossorigin)(="[^"]*"|='[^']*'|=[^"'`=>\s]+|)/ig, '');
+                        }
+                        return m;
+                    });
+                    filter.write(encoder.encode(str));
+                    filter.close();
+                };
+            }
+            return {'responseHeaders': details.responseHeaders};
+
+        }
     }
 };
 
diff --git a/pages/updates/updates.html b/pages/updates/updates.html
index 71ef6186..9fba07a7 100644
--- a/pages/updates/updates.html
+++ b/pages/updates/updates.html
@@ -25,7 +25,7 @@
                         New in LocalCDN:
                     </div>
                     <ul>
-                        <li></li>
+                        <li>Fixed: Check status code in HTML filter (<a href="https://codeberg.org/nobody/LocalCDN/issues/277">#277</a>)</li>
                     </ul>
                     <div id="generator-section">
                         <div class="topic-label">