diff --git a/Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml b/Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml
index bd788b099fc0..67aa7b8fafb8 100644
--- a/Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml
+++ b/Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml
@@ -328,11 +328,11 @@ CSSCustomPropertiesAndValuesEnabled:
   humanReadableDescription: "Enable CSS Custom Properties and Values API"
   defaultValue:
     WebKitLegacy:
-      default: false
+      default: true
     WebKit:
-      default: false
+      default: true
     WebCore:
-      default: false
+      default: true
 
 CSSGradientInterpolationColorSpacesEnabled:
   type: bool