ASSERTION FAILED: name[0] == '@' && length >= 2 in WebCore::CSSTokenizer::detectAtToken

Source/core/css/CSSTokenizer-in.cpp

Index: Source/core/css/CSSTokenizer-in.cpp
diff --git a/Source/core/css/CSSTokenizer-in.cpp b/Source/core/css/CSSTokenizer-in.cpp
index 58a30bc4a0b9ac7c2cd3b44e3ae892e1fb3e3d39..46370a90c985b19530724703169109f26ac49d43 100644
--- a/Source/core/css/CSSTokenizer-in.cpp
+++ b/Source/core/css/CSSTokenizer-in.cpp
@@ -1481,7 +1481,9 @@ restartAfterComment:
             m_token = ATKEYWORD;
             ++result;
             parseIdentifier(result, resultString, hasEscape);
-            detectAtToken<SrcCharacterType>(result - tokenStart<SrcCharacterType>(), hasEscape);
+            // The standard enables unicode escapes in at-rules. In this case only the resultString will contain the
+            // correct identifier, hence we have to use it to determine its length instead of the usual pointer arithmetic.
+            detectAtToken<SrcCharacterType>(resultString.length() + 1, hasEscape);
         }
         break;