diff --git a/sky/engine/wtf/ThreadingPthreads.cpp b/sky/engine/wtf/ThreadingPthreads.cpp
index c3f8671d12b..e67d4b216cf 100644
--- a/sky/engine/wtf/ThreadingPthreads.cpp
+++ b/sky/engine/wtf/ThreadingPthreads.cpp
@@ -28,6 +28,7 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "flutter/sky/engine/wtf/OperatingSystem.h"
 #include "flutter/sky/engine/wtf/Threading.h"
 
 #if USE(PTHREADS)