Matplotlib tight_layout() doesn’t take into account figure suptitle

If I add a subtitle to my matplotlib figure it gets overlaid by the subplot’s titles. Does anybody know how to easily take care of that? I tried the tight_layout() function, but it only makes things worse.

Example:

import numpy as np
import matplotlib.pyplot as plt

f = np.random.random(100)
g = np.random.random(100)
fig = plt.figure()
fig.suptitle('Long Suptitle', fontsize=24)
plt.subplot(121)
plt.plot(f)
plt.title('Very Long Title 1', fontsize=20)
plt.subplot(122)
plt.plot(g)
plt.title('Very Long Title 2', fontsize=20)
plt.tight_layout()
plt.show()