diff --git a/repos/gems/src/lib/tresor/free_tree.cc b/repos/gems/src/lib/tresor/free_tree.cc
index 472a232d26..a22e2f939c 100644
--- a/repos/gems/src/lib/tresor/free_tree.cc
+++ b/repos/gems/src/lib/tresor/free_tree.cc
@@ -216,9 +216,11 @@ void Free_tree::Extend_tree::_generate_write_blk_req(bool &progress)
 }
 
 
-void Free_tree::Extend_tree::_add_new_root_lvl()
+bool Free_tree::Extend_tree::_add_new_root_lvl()
 {
-	ASSERT(_attr.in_out_ft.max_lvl < TREE_MAX_LEVEL);
+	if (_attr.in_out_ft.max_lvl >= TREE_MAX_LEVEL)
+		return false;
+
 	_attr.in_out_ft.max_lvl++;
 	_t1_blks[_attr.in_out_ft.max_lvl] = { };
 	_t1_blks[_attr.in_out_ft.max_lvl].nodes[0] = _attr.in_out_ft.t1_node();
@@ -227,6 +229,8 @@ void Free_tree::Extend_tree::_add_new_root_lvl()
 	if (VERBOSE_FT_EXTENSION)
 		log("  set root: ", _attr.in_out_ft, "\n  set lvl ", _attr.in_out_ft.max_lvl, " node 0: ",
 		    _t1_blks[_attr.in_out_ft.max_lvl].nodes[0]);
+
+	return true;
 }
 
 
@@ -287,7 +291,10 @@ bool Free_tree::Extend_tree::execute(Block_io &block_io, Meta_tree &meta_tree)
 			if (VERBOSE_FT_EXTENSION)
 				log("  root (", _attr.in_out_ft, "): load to lvl ", _lvl);
 		} else {
-			_add_new_root_lvl();
+			if (!_add_new_root_lvl()) {
+				_helper.mark_failed(progress, "failed to add new root level to tree");
+				break;
+			}
 			_add_new_branch_at(_attr.in_out_ft.max_lvl, 1);
 			_generate_write_blk_req(progress);
 			if (VERBOSE_FT_EXTENSION)
diff --git a/repos/gems/src/lib/tresor/include/tresor/free_tree.h b/repos/gems/src/lib/tresor/include/tresor/free_tree.h
index 3f9a434c36..ec710b5a66 100644
--- a/repos/gems/src/lib/tresor/include/tresor/free_tree.h
+++ b/repos/gems/src/lib/tresor/include/tresor/free_tree.h
@@ -154,7 +154,7 @@ class Tresor::Free_tree::Extend_tree : Noncopyable
 
 		void _add_new_branch_at(Tree_level_index, Tree_node_index);
 
-		void _add_new_root_lvl();
+		bool _add_new_root_lvl();
 
 		void _generate_write_blk_req(bool &);
 
diff --git a/repos/gems/src/lib/tresor/include/tresor/virtual_block_device.h b/repos/gems/src/lib/tresor/include/tresor/virtual_block_device.h
index b5df8f4655..ea3d15f46e 100644
--- a/repos/gems/src/lib/tresor/include/tresor/virtual_block_device.h
+++ b/repos/gems/src/lib/tresor/include/tresor/virtual_block_device.h
@@ -282,7 +282,7 @@ class Tresor::Virtual_block_device::Extend_tree : Noncopyable
 		Generatable_request<Helper, State, Block_io::Write> _write_block { };
 		Generatable_request<Helper, State, Free_tree::Allocate_pbas> _alloc_pbas { };
 
-		void _add_new_root_lvl_to_snap();
+		bool _add_new_root_lvl_to_snap();
 
 		void _add_new_branch_to_snap(Tree_level_index, Tree_node_index);
 
diff --git a/repos/gems/src/lib/tresor/virtual_block_device.cc b/repos/gems/src/lib/tresor/virtual_block_device.cc
index 2ffdb87a1b..85ff8ecab3 100644
--- a/repos/gems/src/lib/tresor/virtual_block_device.cc
+++ b/repos/gems/src/lib/tresor/virtual_block_device.cc
@@ -541,7 +541,10 @@ bool Virtual_block_device::Extend_tree::execute(Block_io &block_io, Free_tree &f
 			if (VERBOSE_VBD_EXTENSION)
 				log("  read lvl ", _lvl, " parent snap ", _snap_idx, " ", snap);
 		} else {
-			_add_new_root_lvl_to_snap();
+			if (!_add_new_root_lvl_to_snap()) {
+				_helper.mark_failed(progress, "failed to add new root level to snapshot");
+				break;
+			}
 			_add_new_branch_to_snap(_attr.in_out_snapshots.items[_snap_idx].max_level, 1);
 			_set_new_pbas_identical_to_curr_pbas();
 			_generate_write_blk_req(progress);
@@ -634,12 +637,14 @@ bool Virtual_block_device::Extend_tree::execute(Block_io &block_io, Free_tree &f
 }
 
 
-void Virtual_block_device::Extend_tree::_add_new_root_lvl_to_snap()
+bool Virtual_block_device::Extend_tree::_add_new_root_lvl_to_snap()
 {
 	Snapshot_index old_idx { _snap_idx };
 	Snapshot_index &idx { _snap_idx };
 	Snapshot *snap { _attr.in_out_snapshots.items };
-	ASSERT(snap[idx].max_level < TREE_MAX_LEVEL);
+	if (snap[idx].max_level >= TREE_MAX_LEVEL)
+		return false;
+
 	Tree_level_index new_lvl { snap[old_idx].max_level + 1 };
 	_t1_blks.items[new_lvl] = { };
 	_t1_blks.items[new_lvl].nodes[0] = { snap[idx].pba, snap[idx].gen, snap[idx].hash };
@@ -655,6 +660,8 @@ void Virtual_block_device::Extend_tree::_add_new_root_lvl_to_snap()
 
 	if (VERBOSE_VBD_EXTENSION)
 		log("  update snap ", idx, " ", snap[idx], "\n  update lvl ", new_lvl, " child 0 ", _t1_blks.items[new_lvl].nodes[0]);
+
+	return true;
 }