diff --git a/src/s/hpux.h b/src/s/hpux.h
index 0ddad87e53e..cd15e1ce13d 100644
--- a/src/s/hpux.h
+++ b/src/s/hpux.h
@@ -258,3 +258,6 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 /* This is how to get the device name of the control end of a pty.  */
 #define PTY_NAME_SPRINTF \
 	sprintf (pty_name, "/dev/ptym/pty%c%x", c, i);
+
+/* This triggers a conditional in xfaces.c.  */
+#define XOS_NEEDS_TIME_H
diff --git a/src/s/sol2.h b/src/s/sol2.h
index 1b999aa9509..5255b773dca 100644
--- a/src/s/sol2.h
+++ b/src/s/sol2.h
@@ -1,5 +1,8 @@
 #include "usg5-4.h"
 
+/* This triggers a conditional in xfaces.c.  */
+#define XOS_NEEDS_TIME_H
+
 #define POSIX
 
 /* Here is how to find X Windows.  The -R option says where