diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 7b290ca..c6bc4f9 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -598,6 +598,10 @@ typedef struct MDB_node {
 #define F_BIGDATA	 0x01			/**< data put on overflow page */
 #define F_SUBDATA	 0x02			/**< data is a sub-database */
 #define F_DUPDATA	 0x04			/**< data has duplicates */
+
+/** valid flags for #mdb_node_add() */
+#define	NODE_ADD_FLAGS	(F_DUPDATA|F_SUBDATA|MDB_RESERVE)
+
 /** @} */
 	unsigned short	mn_flags;		/**< @ref mdb_node */
 	unsigned short	mn_ksize;		/**< key size */
@@ -886,7 +890,7 @@ static int  mdb_page_search(MDB_cursor *mc,
 			    MDB_val *key, int modify);
 static int	mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);
 static int	mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
-				pgno_t newpgno);
+				pgno_t newpgno, unsigned int nflags);
 
 static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
 static int  mdb_env_read_meta(MDB_env *env, int *which);
@@ -894,7 +898,7 @@ static int  mdb_env_write_meta(MDB_txn *txn);
 
 static MDB_node *mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp);
 static int  mdb_node_add(MDB_cursor *mc, indx_t indx,
-			    MDB_val *key, MDB_val *data, pgno_t pgno, uint8_t flags);
+			    MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags);
 static void mdb_node_del(MDB_page *mp, indx_t indx, int ksize);
 static void mdb_node_shrink(MDB_page *mp, indx_t indx);
 static int	mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst);
@@ -3875,6 +3879,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 	int rc, rc2;
 	char pbuf[PAGESIZE];
 	char dbuf[MAXKEYSIZE+1];
+	unsigned int nflags;
 	DKBUF;
 
 	if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_RDONLY))
@@ -4068,12 +4073,13 @@ current:
 	rdata = data;
 
 new_sub:
+	nflags = flags & NODE_ADD_FLAGS;
 	nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(mc->mc_txn->mt_env, key, rdata);
 	if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
-		rc = mdb_page_split(mc, key, rdata, P_INVALID);
+		rc = mdb_page_split(mc, key, rdata, P_INVALID, nflags);
 	} else {
 		/* There is room already in this leaf page. */
-		rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, 0);
+		rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
 		if (rc == 0 && !do_sub) {
 			/* Adjust other cursors pointing to mp */
 			MDB_cursor *m2, *m3;
@@ -4100,12 +4106,6 @@ new_sub:
 	if (rc != MDB_SUCCESS)
 		mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
 	else {
-		/* Remember if we just added a subdatabase */
-		if (flags & (F_SUBDATA|F_DUPDATA)) {
-			leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
-			leaf->mn_flags |= (flags & (F_SUBDATA|F_DUPDATA));
-		}
-
 		/* Now store the actual data in the child DB. Note that we're
 		 * storing the user data in the keys field, so there are strict
 		 * size limits on dupdata. The actual data fields of the child
@@ -4117,6 +4117,7 @@ new_sub:
 put_sub:
 			xdata.mv_size = 0;
 			xdata.mv_data = "";
+			leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
 			if (flags & MDB_CURRENT) {
 				xflags = MDB_CURRENT;
 			} else {
@@ -4311,7 +4312,7 @@ mdb_branch_size(MDB_env *env, MDB_val *key)
  */
 static int
 mdb_node_add(MDB_cursor *mc, indx_t indx,
-    MDB_val *key, MDB_val *data, pgno_t pgno, uint8_t flags)
+    MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags)
 {
 	unsigned int	 i;
 	size_t		 node_size = NODESIZE;
@@ -4407,13 +4408,18 @@ mdb_node_add(MDB_cursor *mc, indx_t indx,
 			if (F_ISSET(flags, F_BIGDATA))
 				memcpy(node->mn_data + key->mv_size, data->mv_data,
 				    sizeof(pgno_t));
+			else if (F_ISSET(flags, MDB_RESERVE))
+				data->mv_data = node->mn_data + key->mv_size;
 			else
 				memcpy(node->mn_data + key->mv_size, data->mv_data,
 				    data->mv_size);
 		} else {
 			memcpy(node->mn_data + key->mv_size, &ofp->mp_pgno,
 			    sizeof(pgno_t));
-			memcpy(METADATA(ofp), data->mv_data, data->mv_size);
+			if (F_ISSET(flags, MDB_RESERVE))
+				data->mv_data = METADATA(ofp);
+			else
+				memcpy(METADATA(ofp), data->mv_data, data->mv_size);
 		}
 	}
 
@@ -5219,15 +5225,16 @@ mdb_del(MDB_txn *txn, MDB_dbi dbi,
  * @return 0 on success, non-zero on failure.
  */
 static int
-mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno)
+mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno,
+	unsigned int nflags)
 {
-	uint8_t		 flags;
+	unsigned int flags;
 	int		 rc = MDB_SUCCESS, ins_new = 0, new_root = 0;
 	indx_t		 newindx;
 	pgno_t		 pgno = 0;
 	unsigned int	 i, j, split_indx, nkeys, pmax;
 	MDB_node	*node;
-	MDB_val	 sepkey, rkey, rdata;
+	MDB_val	 sepkey, rkey, xdata, *rdata = &xdata;
 	MDB_page	*copy;
 	MDB_page	*mp, *rp, *pp;
 	unsigned int ptop;
@@ -5385,7 +5392,7 @@ newsep:
 	if (SIZELEFT(mn.mc_pg[ptop]) < mdb_branch_size(mc->mc_txn->mt_env, &sepkey)) {
 		mn.mc_snum--;
 		mn.mc_top--;
-		rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno);
+		rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0);
 
 		/* Right page might now have changed parent.
 		 * Check if left page also changed parent.
@@ -5432,11 +5439,10 @@ newsep:
 			rkey.mv_data = newkey->mv_data;
 			rkey.mv_size = newkey->mv_size;
 			if (IS_LEAF(mp)) {
-				rdata.mv_data = newdata->mv_data;
-				rdata.mv_size = newdata->mv_size;
+				rdata = newdata;
 			} else
 				pgno = newpgno;
-			flags = 0;
+			flags = nflags;
 
 			ins_new = 1;
 
@@ -5449,8 +5455,9 @@ newsep:
 			rkey.mv_data = NODEKEY(node);
 			rkey.mv_size = node->mn_ksize;
 			if (IS_LEAF(mp)) {
-				rdata.mv_data = NODEDATA(node);
-				rdata.mv_size = NODEDSZ(node);
+				xdata.mv_data = NODEDATA(node);
+				xdata.mv_size = NODEDSZ(node);
+				rdata = &xdata;
 			} else
 				pgno = NODEPGNO(node);
 			flags = node->mn_flags;
@@ -5463,7 +5470,7 @@ newsep:
 			rkey.mv_size = 0;
 		}
 
-		rc = mdb_node_add(mc, j, &rkey, &rdata, pgno, flags);
+		rc = mdb_node_add(mc, j, &rkey, rdata, pgno, flags);
 	}
 
 	/* reset back to original page */
@@ -5539,7 +5546,7 @@ mdb_put(MDB_txn *txn, MDB_dbi dbi,
 		return EINVAL;
 	}
 
-	if ((flags & (MDB_NOOVERWRITE|MDB_NODUPDATA)) != flags)
+	if ((flags & (MDB_NOOVERWRITE|MDB_NODUPDATA|MDB_RESERVE)) != flags)
 		return EINVAL;
 
 	mdb_cursor_init(&mc, txn, dbi, &mx);
diff --git a/libraries/libmdb/mdb.h b/libraries/libmdb/mdb.h
index af82e56..3bb7e4c 100644
--- a/libraries/libmdb/mdb.h
+++ b/libraries/libmdb/mdb.h
@@ -189,6 +189,10 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 #define MDB_NODUPDATA	0x20
 /** For mdb_cursor_put: overwrite the current key/data pair */
 #define MDB_CURRENT	0x40
+/** For put: Just reserve space for data, don't copy it. Return a
+ * pointer to the reserved space.
+ */
+#define MDB_RESERVE	0x10000
 /*	@} */
 
 /** @brief Cursor Get operations.