diff --git a/unix/configure.ac b/unix/configure.ac
index 91563562..e1e33acb 100644
--- a/unix/configure.ac
+++ b/unix/configure.ac
@@ -14,6 +14,8 @@ if test "X$GCC" = Xyes; then
     CFLAGS="$CFLAGS -Wall -Werror"
 fi
 
+AC_CHECK_HEADERS([sys/sockio.h],,,[ ])
+
 AM_PATH_GTK([1.2.0], [all_targets="all-cli all-gtk"], [all_targets="all-cli"])
 AC_SUBST([all_targets])
 
diff --git a/unix/uxnet.c b/unix/uxnet.c
index 31b12921..5d4ace44 100644
--- a/unix/uxnet.c
+++ b/unix/uxnet.c
@@ -22,6 +22,11 @@
 #include "network.h"
 #include "tree234.h"
 
+/* Solaris needs <sys/sockio.h> for SIOCATMARK. */
+#ifdef HAVE_SYS_SOCKIO_H
+#include <sys/sockio.h>
+#endif
+
 #ifndef X11_UNIX_PATH
 # define X11_UNIX_PATH "/tmp/.X11-unix/X"
 #endif