diff --git a/sys/sys/param.h b/sys/sys/param.h
index 03323ce03956..a5748c0a8669 100644
--- a/sys/sys/param.h
+++ b/sys/sys/param.h
@@ -331,4 +331,20 @@ __END_DECLS
 #define ctodb(db)			/* calculates pages to devblks */ \
 	((db) << (PAGE_SHIFT - DEV_BSHIFT))
 
+/*
+ * Solaris compatibility definitions.
+ */
+#ifdef _SOLARIS_C_SOURCE
+#define	PAGESIZE	PAGE_SIZE
+
+/*
+ * The OpenSolaris version is set according to the version last imported
+ * from http://dlc.sun.com/osol/on/downloads/current/. In FreeBSD header
+ * files it can be used to detemine the level of compatibility that the
+ * FreeBSD headers provide to OpenSolaris code. Perhaps one day there
+ * will be a really, really Single Unix Specification.
+ */
+#define __OpenSolaris_version 20060731
+#endif
+
 #endif	/* _SYS_PARAM_H_ */