diff --git a/gwsumm/data/coherence.py b/gwsumm/data/coherence.py
index bfe947e5..a6144310 100644
--- a/gwsumm/data/coherence.py
+++ b/gwsumm/data/coherence.py
@@ -290,7 +290,9 @@ def _get_coherence_spectrogram(channel_pair, segments, config=None,
                 globalv.SPECTROGRAMS[key].append(csg)
                 globalv.SPECTROGRAMS[key].coalesce()
             else:
-                warnings.warn('NaN values found in the spectrogram.')
+                warnings.warn('NaN values found in the spectrogram.'
+                                         ' Spectrogram will not be appended to'
+                                         ' global memory value')
 
     if not return_:
         return
diff --git a/gwsumm/data/spectral.py b/gwsumm/data/spectral.py
index 29f8387e..4c434150 100644
--- a/gwsumm/data/spectral.py
+++ b/gwsumm/data/spectral.py
@@ -247,7 +247,9 @@ def add_spectrogram(specgram, key=None, coalesce=True):
         if coalesce:
             globalv.SPECTROGRAMS[key].coalesce()
     else:
-        warnings.warn('NaN values found in the spectrogram.')
+        warnings.warn('NaN values found in the spectrogram.'
+                                 ' Spectrogram will not be appended to'
+                                 ' global memory value')
 
 
 @use_segmentlist