diff --git a/xwords4/relay/permid.h b/xwords4/relay/permid.h
index 29c4bbe1b..0136c4ad0 100644
--- a/xwords4/relay/permid.h
+++ b/xwords4/relay/permid.h
@@ -23,6 +23,7 @@
 #define _PERMID_H
 
 #include <string>
+#include <pthread.h>
 
 /* Able to get a unique ID for every game ever started.  A simple file
  * somewhere stores an ascii string representing a number.  That's
diff --git a/xwords4/relay/timermgr.h b/xwords4/relay/timermgr.h
index c2a69ad9b..52137d47b 100644
--- a/xwords4/relay/timermgr.h
+++ b/xwords4/relay/timermgr.h
@@ -23,6 +23,8 @@
 
 #include "list"
 
+#include <pthread.h>
+
 #include "xwrelay_priv.h"
 
 using namespace std;