--- a/lib/Alembic/Util/Foundation.h
+++ b/lib/Alembic/Util/Foundation.h
@@ -59,6 +59,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <cassert>
+#include <pthread.h>
 
 #include <Alembic/Util/Export.h>