--- a/configure.in
+++ b/configure.in
@@ -94,6 +94,9 @@ dnl statement.
 
 AC_CANONICAL_SYSTEM
 
+dnl Needed for ptsname and friends.
+AC_USE_SYSTEM_EXTENSIONS
+
 dnl In early versions of Solaris, some libraries are in /usr/ccs/lib,
 dnl where gcc doesn't look. The tests below for the curses library
 dnl would thus fail without this directory being added to the search