--- blk.c.orig	Wed Dec  5 08:50:47 1990
+++ blk.c	Wed Dec  4 23:35:36 1996
@@ -19,7 +19,11 @@
 # define NBUFS	5		/* must be at least 3 -- more is better */
 #endif
 
+#if BSD && (BSD >= 199306)
+# include <unistd.h>
+#else
 extern long lseek();
+#endif
 
 /*------------------------------------------------------------------------*/