diff --git a/J/basic.cpp b/J/basic.cpp
index fd8f63f..e981861 100644
--- a/J/basic.cpp
+++ b/J/basic.cpp
@@ -7,6 +7,7 @@
 //
 
 #include "basic.h"
+#include <cassert>
 
 namespace J {
     void check_error(){
diff --git a/J/shader.h b/J/shader.h
index d34cf13..9f6ca94 100644
--- a/J/shader.h
+++ b/J/shader.h
@@ -105,10 +105,11 @@ public:
     // *****************
     // attribute setters
 	// NOTE: the normalized parameter is for integer types, if true they will be mapped to [0, 1], if false it stays in [0, 256] or so.
-    void set_attribute(const std::string& name, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid* ptr){
-        const GLuint index = attributes[name];
-        glVertexAttribPointer(index, size, type, normalized, stride, ptr);
-        glEnableVertexAttribArray(index);
+    void set_attribute(const std::string& name, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid* ptr) const {
+		auto it = attributes.find(name);
+		if(it == attributes.end()) throw std::runtime_error(name + " attribute could not be found");
+        glVertexAttribPointer(it->second, size, type, normalized, stride, ptr);
+        glEnableVertexAttribArray(it->second);
     }
 
     // ***************