diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 945d95d9a7aa..dd112980f08e 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -373,7 +373,7 @@ bufcountwakeup(void)
  *	for earlier writes to complete and generally returns before the
  *	caller's write has reached the device.
  */
-static __inline void
+void
 waitrunningbufspace(void)
 {
 
diff --git a/sys/sys/buf.h b/sys/sys/buf.h
index 6ef4f0f86554..a3dde53a008a 100644
--- a/sys/sys/buf.h
+++ b/sys/sys/buf.h
@@ -478,6 +478,7 @@ extern int	cluster_pbuf_freecnt;	/* Number of pbufs for clusters */
 extern int	vnode_pbuf_freecnt;	/* Number of pbufs for vnode pager */
 
 void	runningbufwakeup(struct buf *);
+void	waitrunningbufspace(void);
 caddr_t	kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est);
 void	bufinit(void);
 void	bwillwrite(void);
diff --git a/sys/ufs/ffs/ffs_snapshot.c b/sys/ufs/ffs/ffs_snapshot.c
index 3e7e2311f0e0..5c62d02ff362 100644
--- a/sys/ufs/ffs/ffs_snapshot.c
+++ b/sys/ufs/ffs/ffs_snapshot.c
@@ -1969,6 +1969,7 @@ ffs_copyonwrite(devvp, bp)
 	struct vnode *vp = 0;
 	ufs2_daddr_t lbn, blkno, *snapblklist;
 	int lower, upper, mid, indiroff, snapshot_locked = 0, error = 0;
+	int launched_async_io, prev_norunningbuf;
 
 	if (td->td_pflags & TDP_COWINPROGRESS)
 		panic("ffs_copyonwrite: recursive call");
@@ -1997,6 +1998,8 @@ ffs_copyonwrite(devvp, bp)
 		VI_UNLOCK(devvp);
 		return (0);
 	}
+	launched_async_io = 0;
+	prev_norunningbuf = td->td_pflags & TDP_NORUNNINGBUF;
 	/*
 	 * Since I/O on bp isn't yet in progress and it may be blocked
 	 * for a long time waiting on snaplk, back it out of
@@ -2101,6 +2104,8 @@ ffs_copyonwrite(devvp, bp)
 			bawrite(cbp);
 			if (dopersistence && ip->i_effnlink > 0)
 				(void) ffs_syncvnode(vp, MNT_WAIT);
+			else
+				launched_async_io = 1;
 			continue;
 		}
 		/*
@@ -2111,6 +2116,8 @@ ffs_copyonwrite(devvp, bp)
 			bawrite(cbp);
 			if (dopersistence && ip->i_effnlink > 0)
 				(void) ffs_syncvnode(vp, MNT_WAIT);
+			else
+				launched_async_io = 1;
 			break;
 		}
 		savedcbp = cbp;
@@ -2125,12 +2132,17 @@ ffs_copyonwrite(devvp, bp)
 		bawrite(savedcbp);
 		if (dopersistence && VTOI(vp)->i_effnlink > 0)
 			(void) ffs_syncvnode(vp, MNT_WAIT);
+		else
+			launched_async_io = 1;
 	}
 	if (snapshot_locked) {
 		lockmgr(vp->v_vnlock, LK_RELEASE, NULL, td);
-		td->td_pflags &= ~TDP_NORUNNINGBUF;
+		td->td_pflags = (td->td_pflags & ~TDP_NORUNNINGBUF) |
+		    prev_norunningbuf;
 	} else
 		VI_UNLOCK(devvp);
+	if (launched_async_io && (td->td_pflags & TDP_NORUNNINGBUF))
+		waitrunningbufspace();
 	/*
 	 * I/O on bp will now be started, so count it in runningbufspace.
 	 */