diff --git a/src/client/GL/GLMatrix.cc b/src/client/GL/GLMatrix.cc
index abcb9dc..99a4916 100644
--- a/src/client/GL/GLMatrix.cc
+++ b/src/client/GL/GLMatrix.cc
@@ -192,7 +192,7 @@ void GLMatrix::ortho(GLfloat left, GLfloat right,
     multiply(mult);
 }
 
-void GLMatrix::to_uniform(GLint uniform)
+void GLMatrix::to_uniform(GLint uniform) const
 {
     glUniformMatrix4fv(uniform, 1, GL_FALSE, &m_mat[0][0]);
 }
diff --git a/src/client/GL/GLMatrix.h b/src/client/GL/GLMatrix.h
index 69db229..f84d324 100644
--- a/src/client/GL/GLMatrix.h
+++ b/src/client/GL/GLMatrix.h
@@ -31,7 +31,7 @@ class GLMatrix
         void ortho(GLfloat left, GLfloat right,
                 GLfloat bottom, GLfloat top,
                 GLfloat z_near, GLfloat z_far);
-        void to_uniform(GLint uniform);
+        void to_uniform(GLint uniform) const;
 
         void push();
         void pop();