diff --git a/Userland/Libraries/LibWeb/CSS/Properties.json b/Userland/Libraries/LibWeb/CSS/Properties.json
index 70da58ff6a..b513822c89 100644
--- a/Userland/Libraries/LibWeb/CSS/Properties.json
+++ b/Userland/Libraries/LibWeb/CSS/Properties.json
@@ -955,6 +955,7 @@
       "percentage"
     ],
     "valid-identifiers": [
+      "auto",
       "none"
     ],
     "quirks": [
@@ -969,6 +970,7 @@
       "percentage"
     ],
     "valid-identifiers": [
+      "auto",
       "none"
     ],
     "quirks": [