Setting Matrices in GLSL Not Working

I have this shader code (GLSL): ` #version 420 ``` in vec4 vertex; uniform mat4 modelViewMatrix; uniform mat4 projectionMatrix; void main() { gl_Position = modelViewMatrix * projectionMatrix * vertex; } ``` ` If I don't set modelViewMatrix and projectionMatrix, it runs without error. If I do, OpenGL throws an Invalid Operation exception when I try to draw. I set the matrices via this code: ` glUniformMatrix4fv(location, 1, false, sendArray);` I have verified that "location" and "sendArray" contain the proper data. What's going on here? EDIT: the problem appears to be in the glUniformMatrix4fv call, but I don't know what's wrong with it. The code to set up `location` is as follows: ` GLint location; ``` GLint location = glGetUniformLocation(this->programID, uniform.c_str()); if (location == -1) { throw ShaderVariableNotFoundException(uniform, this->programID); } ``` `