diff --git a/third_party/blink/renderer/platform/bindings/observable_array.h b/third_party/blink/renderer/platform/bindings/observable_array.h
index d7050727cd..6d3a0b4912 100644
--- a/third_party/blink/renderer/platform/bindings/observable_array.h
+++ b/third_party/blink/renderer/platform/bindings/observable_array.h
@@ -10,6 +10,8 @@
 #include "third_party/blink/renderer/platform/heap/member.h"
 #include "v8/include/v8-forward.h"
 
+#include "third_party/blink/renderer/core/css/css_style_sheet.h"
+
 // Overview of Blink implementation of Web IDL observable arrays
 //
 // Observable arrays are implemented with two objects: