diff --git a/python/fbprophet/forecaster.py b/python/fbprophet/forecaster.py
index d940bd7..e2c18df 100644
--- a/python/fbprophet/forecaster.py
+++ b/python/fbprophet/forecaster.py
@@ -202,7 +202,7 @@ class Prophet(object):
         # convert to days since epoch
         t = np.array(
             (dates - pd.datetime(1970, 1, 1))
-            .apply(lambda x: x.days)
+            .dt.days
             .astype(np.float)
         )
         return np.column_stack([
diff --git a/python/setup.py b/python/setup.py
index 308db20..6cccfc9 100644
--- a/python/setup.py
+++ b/python/setup.py
@@ -83,7 +83,7 @@ setup(
     install_requires=[
         'matplotlib',
         'numpy',
-        'pandas',
+        'pandas>=0.16',
         'pystan>=2.8',
     ],
     zip_safe=False,