drawing a viewport border

I’m using OpenGL to draw a charting app. I have three viewports, two to draw the X and Y axis stuff, the third to draw in the charting area. I draw a box enclosing the third viewport but the box flickers(not the stuff inside just the box) during operation. I am using the following to draw the box.

	glPushMatrix();

	glViewport(50, 50, cx - 100, cy - 100);  // 3rd viewport

        // SetOrtho
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();

        glOrtho( xMin, xMax, yMin, yMax, -zMax, zMax);
	glMatrixMode( GL_MODELVIEW );
	glLoadIdentity();

        // DrawAxisBox
	glLineWidth(1.0f);
	glBegin(GL_LINE_STRIP);
	glVertex3f(xMin, yMin, 0.0f);
	glVertex3f(xMin, yMax, 0.0f);
	glVertex3f(xMax, yMax, 0.0f);
	glVertex3f(xMax, yMin, 0.0f);
	glVertex3f(xMin, yMin, 0.0f);
	glEnd();

	glPopMatrix();
glPushMatrix();
(...)
glMatrixMode(GL_PROJECTION);
(...)
glMatrixMode(GL_MODELVIEW);
(...)
glPopMatrix();

Try moving glPushMatrix after glMatrixMode(GL_MODELVIEW). (before glLoadIdentity).

Thanks for the suggestion but that doesn’t seem to work. I think my problem is that the Box is being clipped by the viewport extents during drawing since I am drawing right on the edge of the viewport. The left edge and bottom of the GL_LINE_STRIP is what’s flickering mostly.