diff --git a/trains/binding/frameworks/tensorflow_bind.py b/trains/binding/frameworks/tensorflow_bind.py
index 52c7ff2b..bc73d632 100644
--- a/trains/binding/frameworks/tensorflow_bind.py
+++ b/trains/binding/frameworks/tensorflow_bind.py
@@ -287,7 +287,16 @@ class EventTrainsWriter(object):
         series = possible_tag or series
         # update scalar cache
         num, value = self._scalar_report_cache.get((title, series), (0, 0))
-        self._scalar_report_cache[(title, series)] = (num + 1, value + scalar_data)
+        # nan outputs is a string, it's probably a NaN
+        if isinstance(scalar_data, six.string_types):
+            try:
+                scalar_data = float(scalar_data)
+            except:
+                scalar_data = float('nan')
+        # nan outputs nan
+        self._scalar_report_cache[(title, series)] = \
+            (num + 1,
+             (value + scalar_data) if scalar_data == scalar_data else scalar_data)
 
         # only report images every specific interval
         if step % self.report_freq != 0: