diff --git a/configure.in b/configure.in
index cd2f280e5ba..6b7c76982bd 100644
--- a/configure.in
+++ b/configure.in
@@ -626,6 +626,7 @@ dnl the qsort routine under solaris is faulty
     DSO_LDOPTS='-Bdynamic'
     MKSHLIB='-$(LD) $(DSO_LDOPTS)'
     MKCSHLIB='-$(LD) $(DSO_LDOPTS)'
+    AC_DEFINE(SUNOS4)
     AC_DEFINE(SPRINTF_RETURNS_STRING)
     ;;