diff --git a/lib/xmet/sounding.py b/lib/xmet/sounding.py
index b890b03..c08d55a 100644
--- a/lib/xmet/sounding.py
+++ b/lib/xmet/sounding.py
@@ -195,6 +195,9 @@ class Sounding(DatabaseTable):
         series = Series()
 
         for sample in self.samples:
+            if sample.dewpoint is None:
+                continue
+
             tv = virtual_temp(sample.temp, sample.dewpoint, sample.pressure)
 
             series[sample.pressure] = tv