diff --git a/code/thinkdsp.py b/code/thinkdsp.py
index 971886a2..5b07acd8 100644
--- a/code/thinkdsp.py
+++ b/code/thinkdsp.py
@@ -934,7 +934,7 @@ def make_spectrogram(self, seg_length, win_flag=True):
         if win_flag:
             window = np.hamming(seg_length)
         i, j = 0, seg_length
-        step = seg_length // 2
+        step = int(seg_length // 2)
 
         # map from time to Spectrum
         spec_map = {}