diff --git a/pygraph/utils/utils.py b/pygraph/utils/utils.py
index 52a85f1..0c7bf60 100644
--- a/pygraph/utils/utils.py
+++ b/pygraph/utils/utils.py
@@ -5,8 +5,8 @@ import numpy as np
 def getSPLengths(G1):
     sp = nx.shortest_path(G1)
     distances = np.zeros((G1.number_of_nodes(), G1.number_of_nodes()))
-    for i in np.keys():
-        for j in np[i].keys():
+    for i in sp.keys():
+        for j in sp[i].keys():
             distances[i, j] = len(sp[i][j])-1
     return distances