diff --git a/packages/engine/Source/Scene/ShadowMapShader.js b/packages/engine/Source/Scene/ShadowMapShader.js
index 7c9744d90c79..fc78fcfdd937 100644
--- a/packages/engine/Source/Scene/ShadowMapShader.js
+++ b/packages/engine/Source/Scene/ShadowMapShader.js
@@ -39,7 +39,7 @@ ShadowMapShader.createShadowCastVertexShader = function (
     }
 
     const shadowVS =
-      "in vec3 v_positionEC; \n" +
+      "out vec3 v_positionEC; \n" +
       "void main() \n" +
       "{ \n" +
       "    czm_shadow_cast_main(); \n" +