diff --git a/ui/gtk/text_import.c b/ui/gtk/text_import.c
index 7108de7634..d4cc7d6b4e 100644
--- a/ui/gtk/text_import.c
+++ b/ui/gtk/text_import.c
@@ -88,8 +88,10 @@
 #  define __USE_XOPEN
 #endif
 #ifndef _XOPEN_SOURCE
-#  ifndef __solaris__
-#    define _XOPEN_SOURCE 600
+#  ifdef __solaris__
+#    define _XOPEN_SOURCE 500	/* 500, for SUSv2; SUSv3 requires c99 */
+#  else
+#    define _XOPEN_SOURCE 600	/* 600, for SUSv3 */
 #  endif
 #endif