diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index ad9ff44802..be009ced55 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -4247,8 +4247,11 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 			MDB_val k2;
 			rc = mdb_cursor_last(mc, &k2, &d2);
 			if (rc == 0) {
-				rc = MDB_NOTFOUND;
-				mc->mc_ki[mc->mc_top]++;
+				rc = mc->mc_dbx->md_cmp(key, &k2);
+				if (rc) {
+					rc = MDB_NOTFOUND;
+					mc->mc_ki[mc->mc_top]++;
+				}
 			}
 		} else {
 		rc = mdb_cursor_set(mc, key, &d2, MDB_SET, &exact);
@@ -4318,6 +4321,7 @@ more:
 				if (mc->mc_db->md_flags & MDB_DUPFIXED) {
 					fp->mp_flags |= P_LEAF2;
 					fp->mp_pad = data->mv_size;
+					fp->mp_upper += 2 * data->mv_size;	/* leave space for 2 more */
 				} else {
 					fp->mp_upper += 2 * sizeof(indx_t) + 2 * NODESIZE +
 						(dkey.mv_size & 1) + (data->mv_size & 1);
@@ -4338,6 +4342,7 @@ more:
 
 				fp = NODEDATA(leaf);
 				if (flags == MDB_CURRENT) {
+reuse:
 					fp->mp_flags |= P_DIRTY;
 					COPY_PGNO(fp->mp_pgno, mc->mc_pg[mc->mc_top]->mp_pgno);
 					mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
@@ -4346,6 +4351,9 @@ more:
 				}
 				if (mc->mc_db->md_flags & MDB_DUPFIXED) {
 					offset = fp->mp_pad;
+					if (SIZELEFT(fp) >= offset)
+						goto reuse;
+					offset *= 4;	/* space for 4 more */
 				} else {
 					offset = NODESIZE + sizeof(indx_t) + data->mv_size;
 				}