diff --git a/ch01/analyze_webstats.py b/ch01/analyze_webstats.py
index 5da892e2..fd052d17 100644
--- a/ch01/analyze_webstats.py
+++ b/ch01/analyze_webstats.py
@@ -81,7 +81,7 @@ def plot_models(x, y, models, fname, mx=None, ymax=None, xmin=None):
     x, y, [f1, f2, f3, f10, f100], os.path.join(CHART_DIR, "1400_01_04.png"))
 
 # fit and plot a model using the knowledge about inflection point
-inflection = 3.5 * 7 * 24
+inflection = int(3.5 * 7 * 24)
 xa = x[:inflection]
 ya = y[:inflection]
 xb = x[inflection:]