3 files changed, 9 insertions, 7 deletions
diff --git a/src/mbgl/algorithm/generate_clip_ids.hpp b/src/mbgl/algorithm/generate_clip_ids.hpp
index adcf87a72a..6950433578 100644
--- a/src/mbgl/algorithm/generate_clip_ids.hpp
+++ b/src/mbgl/algorithm/generate_clip_ids.hpp
@@ -25,8 +25,9 @@ private:
     std::multimap<UnwrappedTileID, Leaf> pool;
 
 public:
+    // The given vector must be sorted by id.
     template <typename Renderable>
-    void update(std::vector<std::reference_wrapper<Renderable>> renderables);
+    void update(std::vector<std::reference_wrapper<Renderable>> sortedRenderables);
 
     std::map<UnwrappedTileID, ClipID> getClipIDs() const;
 };
diff --git a/src/mbgl/algorithm/generate_clip_ids_impl.hpp b/src/mbgl/algorithm/generate_clip_ids_impl.hpp
index fedab06022..a4af9c8cbb 100644
--- a/src/mbgl/algorithm/generate_clip_ids_impl.hpp
+++ b/src/mbgl/algorithm/generate_clip_ids_impl.hpp
@@ -10,12 +10,11 @@ namespace algorithm {
 template <typename Renderable>
 void ClipIDGenerator::update(std::vector<std::reference_wrapper<Renderable>> renderables) {
     std::size_t size = 0;
-
-    std::sort(renderables.begin(), renderables.end(),
-              [](const auto& a, const auto& b) { return a.get().id < b.get().id; });
+    assert(std::is_sorted(renderables.begin(), renderables.end(),
+        [](const Renderable& a, const Renderable& b) { return a.id < b.id; }));
 
     const auto end = renderables.end();
-    for (auto it = renderables.begin(); it != end; it++) {
+    for (auto it = renderables.begin(); it != end; ++it) {
         auto& renderable = it->get();
         if (!renderable.used || !renderable.needsClipping) {
             continue;
diff --git a/src/mbgl/algorithm/update_tile_masks.hpp b/src/mbgl/algorithm/update_tile_masks.hpp
index a7840cd163..c475473cb6 100644
--- a/src/mbgl/algorithm/update_tile_masks.hpp
+++ b/src/mbgl/algorithm/update_tile_masks.hpp
@@ -95,10 +95,12 @@ void computeTileMasks(
 // Only other Renderables that are *children* of the Renderable we are generating the mask for will
 // be considered. For example, adding a Renderable with TileID 4/8/13 won't affect the TileMask for
 // 2/1/3, since it is not a descendant of it.
+//
+// The given |renderables| must be sorted by id.
 template <typename Renderable>
 void updateTileMasks(std::vector<std::reference_wrapper<Renderable>> renderables) {
-    std::sort(renderables.begin(), renderables.end(),
-              [](const Renderable& a, const Renderable& b) { return a.id < b.id; });
+    assert(std::is_sorted(renderables.begin(), renderables.end(),
+        [](const Renderable& a, const Renderable& b) { return a.id < b.id; }));
 
     TileMask mask;
     const auto end = renderables.end();