Rotation Problem


I’m using the mouse to rotate my model around the x and y axis with the following codes:

glRotatef(manualRotateY, 0.0f, 1.0f, 0.0f);
glRotatef(-manualRotateX, 1.0f, 0.0f, 0.0f);

However, after the model is rotated 180 degrees around the y-axis such that the screen is showing the back of the model, rotation around the x-axis is in the opposite direction from when the model is initially at 0 degree. What should I do to make sure they are of the same direction?