diff --git a/platform/mv3/extension/js/scripting/css-generic.js b/platform/mv3/extension/js/scripting/css-generic.js
index 49856ae5f2928..fef6fdf28b147 100644
--- a/platform/mv3/extension/js/scripting/css-generic.js
+++ b/platform/mv3/extension/js/scripting/css-generic.js
@@ -89,8 +89,10 @@ const uBOL_classesFromNode = (node, out) => {
         end = s.indexOf(' ', beg);
         if ( end === beg ) { continue; }
         if ( end === -1 ) { end = len; }
-        out.push(hashFromStr(0x2E /* '.' */, s.slice(beg, end)));
+        const token = s.slice(beg, end).trimEnd();
         beg = end;
+        if ( token.length === 0 ) { continue; }
+        out.push(hashFromStr(0x2E /* '.' */, token));
     }
 };
 
diff --git a/src/js/contentscript.js b/src/js/contentscript.js
index 2af0cabbb16c9..46df837bee235 100644
--- a/src/js/contentscript.js
+++ b/src/js/contentscript.js
@@ -1016,8 +1016,10 @@ vAPI.DOMFilterer = class {
             end = s.indexOf(' ', beg);
             if ( end === beg ) { continue; }
             if ( end === -1 ) { end = len; }
-            const hash = hashFromStr(0x2E /* '.' */, s.slice(beg, end));
+            const token = s.slice(beg, end).trimEnd();
             beg = end;
+            if ( token.length === 0 ) { continue; }
+            const hash = hashFromStr(0x2E /* '.' */, token);
             if ( queriedHashes.has(hash) ) { continue; }
             queriedHashes.add(hash);
             out.push(hash);