diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index 31ab434..c9a82a3 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -279,6 +279,7 @@ var GROUND_BASE_Y = 710;
 var groundCanvas = null;
 var groundCtx = null;
 var groundTexture = null;
+var groundGl = null;        // WebGL context, set by initGroundSystem
 var groundCenterTile = { x: GROUND_BASE_X, y: GROUND_BASE_Y };
 var groundLoadedTiles = {}; // "x_y" -> true
 var groundLastCheck = 0;
@@ -329,9 +330,9 @@ function rebuildGroundMosaic(centerTileX, centerTileY) {
         }
     }
     return Promise.all(promises).then(function() {
-        if (groundTexture) {
-            gl.bindTexture(gl.TEXTURE_2D, groundTexture);
-            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, groundCanvas);
+        if (groundTexture && groundGl) {
+            groundGl.bindTexture(gl.TEXTURE_2D, groundTexture);
+            groundGl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, groundCanvas);
         }
     });
 }
@@ -355,8 +356,9 @@ function maybeRefetchGround(cameraWorldX, cameraWorldZ, gl) {
 
 // Initialise the ground state. Must be called once with the WebGL
 // context before clouds3dRender uses it.
-function initGroundSystem(gl) {
+function initGroundSystem(glCtx) {
     if (groundCanvas) return; // already initialised
+    groundGl = glCtx;
     groundCanvas = document.createElement('canvas');
     groundCanvas.width = GROUND_TILE_SIZE * GROUND_MOSAIC_SIZE;
     groundCanvas.height = GROUND_TILE_SIZE * GROUND_MOSAIC_SIZE;
@@ -365,14 +367,14 @@ function initGroundSystem(gl) {
     // shows the right base colour
     groundCtx.fillStyle = '#7c9aa1';
     groundCtx.fillRect(0, 0, groundCanvas.width, groundCanvas.height);
-    groundTexture = gl.createTexture();
-    gl.bindTexture(gl.TEXTURE_2D, groundTexture);
-    gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
-    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, groundCanvas);
-    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
-    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
-    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
-    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
+    groundTexture = groundGl.createTexture();
+    groundGl.bindTexture(gl.TEXTURE_2D, groundTexture);
+    groundGl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
+    groundGl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, groundCanvas);
+    groundGl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
+    groundGl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+    groundGl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
+    groundGl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
     // Kick off initial fetch
     rebuildGroundMosaic(GROUND_BASE_X, GROUND_BASE_Y);
 }