diff --git a/lib/libc/amd64/sys/ptrace.S b/lib/libc/amd64/sys/ptrace.S
index 9c4628da8ce4..c367a4ea12d1 100644
--- a/lib/libc/amd64/sys/ptrace.S
+++ b/lib/libc/amd64/sys/ptrace.S
@@ -38,14 +38,16 @@ __FBSDID("$FreeBSD$");
 
 #include "SYS.h"
 
+	.globl	CNAME(__error)
+	.type	CNAME(__error),@function
+
 ENTRY(ptrace)
-	xorl	%eax,%eax
 #ifdef PIC
-	movq	PIC_GOT(CNAME(errno)),%r8
-	movl	%eax,(%r8)
+	callq	PIC_PLT(CNAME(__error))
 #else
-	movl	%eax,CNAME(errno)(%rip)
+	callq	CNAME(__error)
 #endif
+	movl	$0,(%rax)
 	mov	$SYS_ptrace,%eax
 	KERNCALL
 	jb	HIDENAME(cerror)
diff --git a/lib/libc/i386/sys/ptrace.S b/lib/libc/i386/sys/ptrace.S
index e4bdf7cd28ff..d1942975fcd0 100644
--- a/lib/libc/i386/sys/ptrace.S
+++ b/lib/libc/i386/sys/ptrace.S
@@ -38,16 +38,18 @@ __FBSDID("$FreeBSD$");
 
 #include "SYS.h"
 
+	.globl	CNAME(__error)
+	.type	CNAME(__error),@function
+
 ENTRY(ptrace)
-	xorl	%eax,%eax
 #ifdef PIC
-        PIC_PROLOGUE
-        movl    PIC_GOT(CNAME(errno)),%edx
-        movl    %eax,(%edx)
-        PIC_EPILOGUE
+	PIC_PROLOGUE
+	call	PIC_PLT(CNAME(__error))
+	PIC_EPILOGUE
 #else
-        movl    %eax,CNAME(errno)
+	call	CNAME(__error)
 #endif
+	movl	$0,(%eax)
 	mov	$SYS_ptrace,%eax
 	KERNCALL
 	jb	HIDENAME(cerror)
diff --git a/lib/libc/sys/ptrace.2 b/lib/libc/sys/ptrace.2
index 74798d27cfff..48802f42457e 100644
--- a/lib/libc/sys/ptrace.2
+++ b/lib/libc/sys/ptrace.2
@@ -2,7 +2,7 @@
 .\"	$NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $
 .\"
 .\" This file is in the public domain.
-.Dd July 28, 2016
+.Dd August 28, 2016
 .Dt PTRACE 2
 .Os
 .Sh NAME
@@ -906,7 +906,13 @@ to return
 \-1
 as a non-error value; to disambiguate,
 .Va errno
-can be set to 0 before the call and checked afterwards.
+is set to 0 in the libc wrapper for the
+.Fn ptrace
+system call and
+.Fn ptrace
+callers can reliably check
+.Va errno
+for non-zero value afterwards.
 .Sh ERRORS
 The
 .Fn ptrace