diff --git a/src/s/irix5-0.h b/src/s/irix5-0.h
index 4b5ec36396e..9e21963125e 100644
--- a/src/s/irix5-0.h
+++ b/src/s/irix5-0.h
@@ -123,3 +123,4 @@ char *_getpty();
 
 #define NARROWPROTO 1
 
+#define REL_ALLOC_MMAP 1
diff --git a/src/s/sol2.h b/src/s/sol2.h
index d0c42e6c62c..a53ac8bdbaf 100644
--- a/src/s/sol2.h
+++ b/src/s/sol2.h
@@ -46,3 +46,5 @@
 #ifndef TERMINFO
 #define LIBS_TERMCAP -ltermcap
 #endif
+
+#define REL_ALLOC_MMAP 1