diff --git a/impl/utils/plot_constellation.py b/impl/utils/plot_constellation.py
index d79de51..13bc046 100755
--- a/impl/utils/plot_constellation.py
+++ b/impl/utils/plot_constellation.py
@@ -15,4 +15,13 @@ with open(sys.argv[1], 'rb') as infile:
     data = np.fromfile(infile, dtype=np.complex64)
 
     pp.plot(np.real(data), np.imag(data), 'x')
+
+    a = np.linspace(-np.pi, np.pi, 200)
+    pp.plot(np.cos(a), np.sin(a), 'k--', linewidth=0.7)
+    pp.plot([1, 1, -1, -1, 1], [1, -1, -1, 1, 1], 'k--', linewidth=0.7)
+    pp.plot([-1.5, 1.5], [0, 0], 'k--', linewidth=0.7)
+    pp.plot([0, 0], [-1.5, 1.5], 'k--', linewidth=0.7)
+    pp.xlim([-1.5, 1.5])
+    pp.ylim([-1.5, 1.5])
+    pp.axis('equal')
     pp.show()