diff --git a/src/s/sunos413.h b/src/s/sunos413.h
index 39ade191e571de158cdb3db6ed886c1f58fcc903..d5dec97665f9aeb93ff54027c9b7bc163be97f76 100644
--- a/src/s/sunos413.h
+++ b/src/s/sunos413.h
@@ -19,3 +19,7 @@
 #ifndef SYSTEM_MALLOC
 #define MEMMOVE_MISSING
 #endif
+
+/* brett@kirk.es.go.dlr.de reported that, without this definition,
+   Emacs would loop when olvwm exits.  */
+#define X_IO_BUG