diff --git a/usr.bin/top/commands.c b/usr.bin/top/commands.c
index c08f70a0fe54..d6e0714a32cc 100644
--- a/usr.bin/top/commands.c
+++ b/usr.bin/top/commands.c
@@ -18,14 +18,15 @@
  *  "top" (i.e.:  changing the number of processes to display).
  */
 
-#include "os.h"
-
 #include <sys/time.h>
 #include <sys/resource.h>
 
 #include <ctype.h>
 #include <errno.h>
 #include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 
 #include "commands.h"
diff --git a/usr.bin/top/display.c b/usr.bin/top/display.c
index 5d938df7e387..662cb6bf60fc 100644
--- a/usr.bin/top/display.c
+++ b/usr.bin/top/display.c
@@ -28,12 +28,13 @@
  *        *_process, u_endscreen.
  */
 
-#include "os.h"
-
 #include <sys/time.h>
 
 #include <curses.h>
 #include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
 #include <termcap.h>
 #include <time.h>
 #include <unistd.h>
@@ -927,7 +928,7 @@ char *thisline;
     p = strecpy(base, thisline);
 
     /* zero fill the rest of it */
-    memzero(p, display_width - (p - base));
+    bzero(p, display_width - (p - base));
 }
 
 void
@@ -970,7 +971,7 @@ char *newline;
 	optr = strecpy(bufferline, newline);
 
 	/* zero fill the rest of it */
-	memzero(optr, display_width - (optr - bufferline));
+	bzero(optr, display_width - (optr - bufferline));
     }
     else
     {
@@ -1381,7 +1382,7 @@ int line;
     diff = display_width - newcol;
     if (diff > 0)
     {
-	memzero(old, diff);
+	bzero(old, diff);
     }
 
     /* remember where the current line is */
diff --git a/usr.bin/top/os.h b/usr.bin/top/os.h
deleted file mode 100644
index 8316a4c5bb1c..000000000000
--- a/usr.bin/top/os.h
+++ /dev/null
@@ -1,38 +0,0 @@
-#include <sys/types.h>
-#include <sys/param.h>	/* This defines BSD */
-#if defined(BSD) && !defined(BSD4_4) && !defined(__osf__)
-# include <stdio.h>
-# include <strings.h>
-# define strchr(a, b)		index((a), (b))
-# define strrchr(a, b)		rindex((a), (b))
-# define memcpy(a, b, c)	bcopy((b), (a), (c))
-# define memzero(a, b)		bzero((a), (b))
-# define memcmp(a, b, c)	bcmp((a), (b), (c))
-#if defined(NeXT)
-  typedef void sigret_t;
-#else
-  typedef int sigret_t;
-#endif
-
-/* system routines that don't return int */
-char *getenv();
-caddr_t malloc();
-
-#else 
-# include <stdio.h>
-# define setbuffer(f, b, s)	setvbuf((f), (b), (b) ? _IOFBF : _IONBF, (s))
-# include <string.h>
-# include <memory.h>
-# include <stdlib.h>
-# define memzero(a, b)		memset((a), 0, (b))
-  typedef void sigret_t;
-#endif
-
-/* some systems declare sys_errlist in stdio.h! */
-#if defined(__NetBSD__) || defined(__FreeBSD__)
-#if !defined(__m68k__)
-#  if !defined(__NetBSD132__)
-#define SYS_ERRLIST_DECLARED
-#  endif	/* __NetBSD132__ */
-#endif
-#endif
diff --git a/usr.bin/top/screen.c b/usr.bin/top/screen.c
index 7ee9038cfc68..aeb9daf6d8ce 100644
--- a/usr.bin/top/screen.c
+++ b/usr.bin/top/screen.c
@@ -20,10 +20,10 @@
  *  preprocessor variable "TOStop".   --wnl
  */
 
-#include "os.h"
 #include "top.h"
 
 #include <sys/ioctl.h>
+#include <string.h>
 #ifdef CBREAK
 # include <sgtty.h>
 # define SGTTY
diff --git a/usr.bin/top/top.c b/usr.bin/top/top.c
index 193bca8e4644..1c48dfee7945 100644
--- a/usr.bin/top/top.c
+++ b/usr.bin/top/top.c
@@ -33,8 +33,8 @@ char *copyright =
  *	FD_SET   - macros FD_SET and FD_ZERO are used when defined
  */
 
-#include "os.h"
-
+#include <sys/types.h>
+#include <sys/param.h>
 #include <sys/jail.h>
 #include <sys/time.h>
 
@@ -43,7 +43,9 @@ char *copyright =
 #include <errno.h>
 #include <jail.h>
 #include <setjmp.h>
+#include <stdlib.h>
 #include <signal.h>
+#include <string.h>
 #include <unistd.h>
 
 /* includes specific to top */
@@ -60,6 +62,8 @@ char *copyright =
 /* Size of the stdio buffer given to stdout */
 #define Buffersize	2048
 
+typedef void sigret_t;
+
 /* The buffer that stdio will use */
 char stdoutbuf[Buffersize];
 
diff --git a/usr.bin/top/utils.c b/usr.bin/top/utils.c
index ba8c3f1b752f..605b50afeedc 100644
--- a/usr.bin/top/utils.c
+++ b/usr.bin/top/utils.c
@@ -16,7 +16,10 @@
  */
 
 #include "top.h"
-#include "os.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
 
 int atoiwi(str)