diff --git a/backends/graphics/opengl/shader.cpp b/backends/graphics/opengl/shader.cpp
index 71cdf544a88..0cee3a737cd 100644
--- a/backends/graphics/opengl/shader.cpp
+++ b/backends/graphics/opengl/shader.cpp
@@ -118,6 +118,7 @@ Shader *ShaderManager::query(ShaderUsage shader) const {
 		return nullptr;
 	}
 
+	assert(_builtIn[shader]);
 	return _builtIn[shader]->clone();
 }