Index: sys/compat/freebsd32/freebsd32_misc.c
===================================================================
--- sys/compat/freebsd32/freebsd32_misc.c
+++ sys/compat/freebsd32/freebsd32_misc.c
@@ -2965,21 +2965,22 @@
 freebsd32_posix_fallocate(struct thread *td,
     struct freebsd32_posix_fallocate_args *uap)
 {
+	int error;
 
-	td->td_retval[0] = kern_posix_fallocate(td, uap->fd,
+	error = kern_posix_fallocate(td, uap->fd,
 	    PAIR32TO64(off_t, uap->offset), PAIR32TO64(off_t, uap->len));
-	return (0);
+	return (kern_posix_error(td, error));
 }
 
 int
 freebsd32_posix_fadvise(struct thread *td,
     struct freebsd32_posix_fadvise_args *uap)
 {
+	int error;
 
-	td->td_retval[0] = kern_posix_fadvise(td, uap->fd,
-	    PAIR32TO64(off_t, uap->offset), PAIR32TO64(off_t, uap->len),
-	    uap->advice);
-	return (0);
+	error = kern_posix_fadvise(td, uap->fd, PAIR32TO64(off_t, uap->offset),
+	    PAIR32TO64(off_t, uap->len), uap->advice);
+	return (kern_posix_error(td, error));
 }
 
 int
Index: sys/kern/sys_generic.c
===================================================================
--- sys/kern/sys_generic.c
+++ sys/kern/sys_generic.c
@@ -1910,3 +1910,19 @@
 	    NULL, NULL, UMA_ALIGN_PTR, 0);
 	mtxpool_select = mtx_pool_create("select mtxpool", 128, MTX_DEF);
 }
+
+/*
+ * Set up a syscall return value that follows the convention specified for
+ * posix_* functions.
+ */
+int
+kern_posix_error(struct thread *td, int error)
+{
+
+	if (error <= 0)
+		return (error);
+	td->td_errno = error;
+	td->td_pflags |= TDP_NERRNO;
+	td->td_retval[0] = error;
+	return (0);
+}
Index: sys/kern/vfs_syscalls.c
===================================================================
--- sys/kern/vfs_syscalls.c
+++ sys/kern/vfs_syscalls.c
@@ -4533,10 +4533,10 @@
 int
 sys_posix_fallocate(struct thread *td, struct posix_fallocate_args *uap)
 {
+	int error;
 
-	td->td_retval[0] = kern_posix_fallocate(td, uap->fd, uap->offset,
-	    uap->len);
-	return (0);
+	error = kern_posix_fallocate(td, uap->fd, uap->offset, uap->len);
+	return (kern_posix_error(td, error));
 }
 
 /*
@@ -4668,8 +4668,9 @@
 int
 sys_posix_fadvise(struct thread *td, struct posix_fadvise_args *uap)
 {
+	int error;
 
-	td->td_retval[0] = kern_posix_fadvise(td, uap->fd, uap->offset,
-	    uap->len, uap->advice);
-	return (0);
+	error = kern_posix_fadvise(td, uap->fd, uap->offset, uap->len,
+	    uap->advice);
+	return (kern_posix_error(td, error));
 }
Index: sys/sys/syscallsubr.h
===================================================================
--- sys/sys/syscallsubr.h
+++ sys/sys/syscallsubr.h
@@ -158,6 +158,7 @@
 	    struct filecaps *fcaps1, struct filecaps *fcaps2);
 int	kern_poll(struct thread *td, struct pollfd *fds, u_int nfds,
 	    struct timespec *tsp, sigset_t *uset);
+int	kern_posix_error(struct thread *td, int error);
 int	kern_posix_fadvise(struct thread *td, int fd, off_t offset, off_t len,
 	    int advice);
 int	kern_posix_fallocate(struct thread *td, int fd, off_t offset,