diff --git a/genesis/ext/pyrender/primitive.py b/genesis/ext/pyrender/primitive.py
index 580880498c..8f631d81cf 100644
--- a/genesis/ext/pyrender/primitive.py
+++ b/genesis/ext/pyrender/primitive.py
@@ -478,7 +478,7 @@ def _remove_from_context(self):
             glDeleteVertexArrays(1, [self._vaid])
             glDeleteBuffers(len(self._buffers), list(self._buffers.values()))
             self._vaid = None
-            self._buffers = {}
+            self._buffers.clear()
 
     def _in_context(self):
         return self._vaid is not None
diff --git a/genesis/ext/pyrender/renderer.py b/genesis/ext/pyrender/renderer.py
index 2c31db13b7..28c26cc091 100644
--- a/genesis/ext/pyrender/renderer.py
+++ b/genesis/ext/pyrender/renderer.py
@@ -609,24 +609,26 @@ def _bind_and_draw_primitive(self, primitive, pose, program, flags, env_idx):
     ###########################################################################
 
     def _update_context(self, scene, flags):
-        # Update meshes
-        scene_meshes = scene.meshes
+        # Get existing and new meshes
+        scene_meshes_new = scene.meshes.copy()
+        scene_meshes_old = self._meshes
 
-        # Add new meshes to context
-        for mesh in scene_meshes - self._meshes:
-            for p in mesh.primitives:
-                p._add_to_context()
-
-        # Remove old meshes from context
-        for mesh in self._meshes - scene_meshes:
+        # Remove from context old meshes that are now irrelevant
+        for mesh in scene_meshes_old - scene_meshes_new:
             for p in mesh.primitives:
                 p.delete()
 
-        self._meshes = scene_meshes.copy()
+        # Update set of meshes right away, so that the context can be cleaned up correctly in case of failure
+        self._meshes = scene_meshes_new
+
+        # Add new meshes to context
+        for mesh in scene_meshes_new - scene_meshes_old:
+            for p in mesh.primitives:
+                p._add_to_context()
 
         # Update mesh textures
         mesh_textures = set()
-        for m in scene_meshes:
+        for m in scene_meshes_new:
             for p in m.primitives:
                 mesh_textures |= p.material.textures
 
diff --git a/genesis/ext/pyrender/viewer.py b/genesis/ext/pyrender/viewer.py
index d21714ff3c..9b6adf081c 100644
--- a/genesis/ext/pyrender/viewer.py
+++ b/genesis/ext/pyrender/viewer.py
@@ -1237,7 +1237,7 @@ def start(self, auto_refresh=True):
         except OpenGL.error.Error:
             # Invalid OpenGL context. Closing before raising.
             self.close()
-            return
+            raise
 
         # At this point, we are all set to display the graphical window, finally!
         self.set_visible(True)