diff --git a/auxprogs/valgrind-di-server.c b/auxprogs/valgrind-di-server.c
index 06dfdf8..f7a0ba0 100644
--- a/auxprogs/valgrind-di-server.c
+++ b/auxprogs/valgrind-di-server.c
@@ -88,6 +88,9 @@
                                     // pub_core_libcfile.h
 #include "pub_core_libcfile.h"      // For VG_CLO_DEFAULT_LOGPORT
 
+/* Needed to get a definition for pread() from unistd.h */
+#define _XOPEN_SOURCE 500
+
 #include <stdio.h>
 #include <unistd.h>
 #include <string.h>