diff --git a/asymptote/runhistory.cc b/asymptote/runhistory.cc
index 910113d..4155459 100644
--- a/asymptote/runhistory.cc
+++ b/asymptote/runhistory.cc
@@ -1,5 +1,7 @@
 /***** Autogenerated from runhistory.in; changes will be overwritten *****/
 
+#include <unistd.h>
+
 #line 1 "runtimebase.in"
 /*****
  * runtimebase.in