diff --git a/R/R/prophet.R b/R/R/prophet.R
index 19436a3..6318d04 100644
--- a/R/R/prophet.R
+++ b/R/R/prophet.R
@@ -169,6 +169,9 @@ validate_inputs <- function(m) {
       stop('Holidays dataframe must have ds field.')
     }
     m$holidays$ds <- as.Date(m$holidays$ds)
+    if (any(is.na(m$holidays))) {
+      stop('Found NA in the holidays dataframe.')
+    }
     has.lower <- exists('lower_window', where = m$holidays)
     has.upper <- exists('upper_window', where = m$holidays)
     if (has.lower + has.upper == 1) {
diff --git a/python/fbprophet/forecaster.py b/python/fbprophet/forecaster.py
index 40386c3..038ff8c 100644
--- a/python/fbprophet/forecaster.py
+++ b/python/fbprophet/forecaster.py
@@ -169,6 +169,8 @@ class Prophet(object):
                 raise ValueError('holidays must be a DataFrame with "ds" and '
                                  '"holiday" columns.')
             self.holidays['ds'] = pd.to_datetime(self.holidays['ds'])
+            if self.holidays.isnull().any().any():
+                raise ValueError('Found a NaN in holidays dataframe')
             has_lower = 'lower_window' in self.holidays
             has_upper = 'upper_window' in self.holidays
             if has_lower + has_upper == 1: