diff --git a/R/R/prophet.R b/R/R/prophet.R
index 6d36854..2eb4e46 100644
--- a/R/R/prophet.R
+++ b/R/R/prophet.R
@@ -1379,6 +1379,9 @@ make_future_dataframe <- function(m, periods, freq = 'day',
   if (freq == 'm') {
     freq <- 'month'
   }
+  if (is.null(m$history.dates)) {
+    stop('Model must be fit before this can be used.')
+  }
   dates <- seq(max(m$history.dates), length.out = periods + 1, by = freq)
   dates <- dates[2:(periods + 1)]  # Drop the first, which is max(history$ds)
   if (include_history) {
diff --git a/python/fbprophet/forecaster.py b/python/fbprophet/forecaster.py
index 96937e9..d3cefc8 100644
--- a/python/fbprophet/forecaster.py
+++ b/python/fbprophet/forecaster.py
@@ -1214,6 +1214,8 @@ class Prophet(object):
         pd.Dataframe that extends forward from the end of self.history for the
         requested number of periods.
         """
+        if self.history_dates is None:
+            raise Exception('Model must be fit before this can be used.')
         last_date = self.history_dates.max()
         dates = pd.date_range(
             start=last_date,