diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 2a7ca54d83..80336831e1 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1941,7 +1941,7 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 		unsigned int i;
 		txn->mt_u.dirty_list = malloc(sizeof(MDB_ID2)*MDB_IDL_UM_SIZE);
 		if (!txn->mt_u.dirty_list ||
-			!(txn->mt_free_pgs = mdb_midl_alloc()))
+			!(txn->mt_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)))
 		{
 			free(txn->mt_u.dirty_list);
 			free(txn);
@@ -3472,7 +3472,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode
 		/* silently ignore WRITEMAP when we're only getting read access */
 		flags &= ~MDB_WRITEMAP;
 	} else {
-		if (!((env->me_free_pgs = mdb_midl_alloc()) &&
+		if (!((env->me_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)) &&
 			  (env->me_dirty_list = calloc(MDB_IDL_UM_SIZE, sizeof(MDB_ID2)))))
 			rc = ENOMEM;
 	}
diff --git a/libraries/liblmdb/midl.c b/libraries/liblmdb/midl.c
index 8020edc0ae..42c809fd4d 100644
--- a/libraries/liblmdb/midl.c
+++ b/libraries/liblmdb/midl.c
@@ -117,16 +117,18 @@ int mdb_midl_insert( MDB_IDL ids, MDB_ID id )
 }
 #endif
 
-MDB_IDL mdb_midl_alloc(void)
+MDB_IDL mdb_midl_alloc(int num)
 {
-	MDB_IDL ids = malloc((MDB_IDL_UM_MAX+1) * sizeof(MDB_ID));
-	*ids++ = MDB_IDL_UM_MAX;
+	MDB_IDL ids = malloc((num+2) * sizeof(MDB_ID));
+	if (ids)
+		*ids++ = num;
 	return ids;
 }
 
 void mdb_midl_free(MDB_IDL ids)
 {
-	free(ids-1);
+	if (ids)
+		free(ids-1);
 }
 
 int mdb_midl_shrink( MDB_IDL *idp )
@@ -141,19 +143,26 @@ int mdb_midl_shrink( MDB_IDL *idp )
 	return 0;
 }
 
+int mdb_midl_grow( MDB_IDL *idp, int num )
+{
+	MDB_IDL idn = *idp-1;
+	/* grow it */
+	idn = realloc(idn, (*idn + num + 2) * sizeof(MDB_ID));
+	if (!idn)
+		return ENOMEM;
+	*idn++ += num;
+	*idp = idn;
+	return 0;
+}
+
 int mdb_midl_append( MDB_IDL *idp, MDB_ID id )
 {
 	MDB_IDL ids = *idp;
 	/* Too big? */
 	if (ids[0] >= ids[-1]) {
-		MDB_IDL idn = ids-1;
-		/* grow it */
-		idn = realloc(idn, (*idn + MDB_IDL_UM_MAX + 1) * sizeof(MDB_ID));
-		if (!idn)
-			return -1;
-		*idn++ += MDB_IDL_UM_MAX;
-		ids = idn;
-		*idp = ids;
+		if (mdb_midl_grow(idp, MDB_IDL_UM_MAX))
+			return ENOMEM;
+		ids = *idp;
 	}
 	ids[0]++;
 	ids[ids[0]] = id;
@@ -165,14 +174,9 @@ int mdb_midl_append_list( MDB_IDL *idp, MDB_IDL app )
 	MDB_IDL ids = *idp;
 	/* Too big? */
 	if (ids[0] + app[0] >= ids[-1]) {
-		MDB_IDL idn = ids-1;
-		/* grow it */
-		idn = realloc(idn, (*idn + app[-1]) * sizeof(MDB_ID));
-		if (!idn)
-			return -1;
-		*idn++ += app[-1];
-		ids = idn;
-		*idp = ids;
+		if (mdb_midl_grow(idp, app[0]))
+			return ENOMEM;
+		ids = *idp;
 	}
 	memcpy(&ids[ids[0]+1], &app[1], app[0] * sizeof(MDB_ID));
 	ids[0] += app[0];
diff --git a/libraries/liblmdb/midl.h b/libraries/liblmdb/midl.h
index a284223ab3..9319fb590b 100644
--- a/libraries/liblmdb/midl.h
+++ b/libraries/liblmdb/midl.h
@@ -115,10 +115,10 @@ int mdb_midl_insert( MDB_IDL ids, MDB_ID id );
 #endif
 
 	/** Allocate an IDL.
-	 * Allocates memory for an IDL of a default size.
+	 * Allocates memory for an IDL of the given size.
 	 * @return	IDL on success, NULL on failure.
 	 */
-MDB_IDL mdb_midl_alloc(void);
+MDB_IDL mdb_midl_alloc(int num);
 
 	/** Free an IDL.
 	 * @param[in] ids	The IDL to free.
@@ -132,6 +132,14 @@ void mdb_midl_free(MDB_IDL ids);
 	 */
 int mdb_midl_shrink(MDB_IDL *idp);
 
+	/** Grow an IDL.
+	 * Add room for num additional elements.
+	 * @param[in,out] idp	Address of the IDL to grow.
+	 * @param[i] num	Number of elements to add.
+	 * @return	0 on success, -1 on failure.
+	 */
+int mdb_midl_grow(MDB_IDL *idp, int num);
+
 	/** Append an ID onto an IDL.
 	 * @param[in,out] idp	Address of the IDL to append to.
 	 * @param[in] id	The ID to append.