diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 47a5036..4e23888 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1940,7 +1940,7 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 	MDB_txn *txn = mc->mc_txn;
 	MDB_env *env = txn->mt_env;
 	pgno_t pgno, *mop = env->me_pghead;
-	unsigned i, j, k, mop_len = mop ? mop[0] : 0, n2 = num-1;
+	unsigned i, j, mop_len = mop ? mop[0] : 0, n2 = num-1;
 	MDB_page *np;
 	txnid_t oldest = 0, last;
 	MDB_cursor_op op;
@@ -1967,7 +1967,7 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 	for (op = MDB_FIRST;; op = MDB_NEXT) {
 		MDB_val key, data;
 		MDB_node *leaf;
-		pgno_t *idl, old_id, new_id;
+		pgno_t *idl;
 
 		/* Seek a big enough contiguous page range. Prefer
 		 * pages at the tail, just truncating the list.
@@ -2033,21 +2033,12 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 #if (MDB_DEBUG) > 1
 		DPRINTF(("IDL read txn %"Z"u root %"Z"u num %u",
 			last, txn->mt_dbs[FREE_DBI].md_root, i));
-		for (k = i; k; k--)
-			DPRINTF(("IDL %"Z"u", idl[k]));
+		for (j = i; j; j--)
+			DPRINTF(("IDL %"Z"u", idl[j]));
 #endif
 		/* Merge in descending sorted order */
-		j = mop_len;
-		k = mop_len += i;
-		mop[0] = (pgno_t)-1;
-		old_id = mop[j];
-		while (i) {
-			new_id = idl[i--];
-			for (; old_id < new_id; old_id = mop[--j])
-				mop[k--] = old_id;
-			mop[k--] = new_id;
-		}
-		mop[0] = mop_len;
+		mdb_midl_xmerge(mop, idl);
+		mop_len = mop[0];
 	}
 
 	/* Use new pages from the map when nothing suitable in the freeDB */
diff --git a/libraries/liblmdb/midl.c b/libraries/liblmdb/midl.c
index d3d872a..88a3aff 100644
--- a/libraries/liblmdb/midl.c
+++ b/libraries/liblmdb/midl.c
@@ -199,6 +199,20 @@ int mdb_midl_append_range( MDB_IDL *idp, MDB_ID id, unsigned n )
 	return 0;
 }
 
+void mdb_midl_xmerge( MDB_IDL idl, MDB_IDL merge )
+{
+	MDB_ID old_id, merge_id, i = merge[0], j = idl[0], k = i+j, total = k;
+	idl[0] = (MDB_ID)-1;		/* delimiter for idl scan below */
+	old_id = idl[j];
+	while (i) {
+		merge_id = merge[i--];
+		for (; old_id < merge_id; old_id = idl[--j])
+			idl[k--] = old_id;
+		idl[k--] = merge_id;
+	}
+	idl[0] = total;
+}
+
 /* Quicksort + Insertion sort for small arrays */
 
 #define SMALL	8
diff --git a/libraries/liblmdb/midl.h b/libraries/liblmdb/midl.h
index 08616f4..a7f2502 100644
--- a/libraries/liblmdb/midl.h
+++ b/libraries/liblmdb/midl.h
@@ -68,6 +68,9 @@ typedef MDB_ID *MDB_IDL;
 #define MDB_IDL_FIRST( ids )	( (ids)[1] )
 #define MDB_IDL_LAST( ids )		( (ids)[(ids)[0]] )
 
+	/** Current max length of an #mdb_midl_alloc()ed IDL */
+#define MDB_IDL_ALLOCLEN( ids )	( (ids)[-1] )
+
 	/** Append ID to IDL. The IDL must be big enough. */
 #define mdb_midl_xappend(idl, id) do { \
 		MDB_ID *xidl = (idl), xlen = ++(xidl[0]); \
@@ -128,6 +131,12 @@ int mdb_midl_append_list( MDB_IDL *idp, MDB_IDL app );
 	 */
 int mdb_midl_append_range( MDB_IDL *idp, MDB_ID id, unsigned n );
 
+	/** Merge an IDL onto an IDL. The destination IDL must be big enough.
+	 * @param[in] idl	The IDL to merge into.
+	 * @param[in] merge	The IDL to merge.
+	 */
+void mdb_midl_xmerge( MDB_IDL idl, MDB_IDL merge );
+
 	/** Sort an IDL.
 	 * @param[in,out] ids	The IDL to sort.
 	 */