diff --git a/tests/gpulightmap.html b/tests/gpulightmap.html
index 0bfca00..e6a9396 100644
--- a/tests/gpulightmap.html
+++ b/tests/gpulightmap.html
@@ -31,6 +31,10 @@
   document.write('This demo requires the OES_texture_float extension to run');
   throw 'not supported';
 }
+if (!gl.getExtension('OES_texture_float_linear')) {
+  document.write('This demo requires the OES_texture_float_linear extension to run');
+  throw 'not supported';
+}
 
 var depthMap = new GL.Texture(1024, 1024, { format: gl.RED });
 var depthShader = new GL.Shader('\