diff --git a/gwsumm/data/coherence.py b/gwsumm/data/coherence.py
index 6a1f7c2b..f3a2a4dc 100644
--- a/gwsumm/data/coherence.py
+++ b/gwsumm/data/coherence.py
@@ -286,8 +286,13 @@ def _get_coherence_spectrogram(channel_pair, segments, config=None,
             cxy, cxx, cyy = [_get_from_list(
                 globalv.COHERENCE_COMPONENTS[ck], seg) for ck in ckeys]
             csg = abs(cxy)**2 / cxx / cyy
-            globalv.SPECTROGRAMS[key].append(csg)
-            globalv.SPECTROGRAMS[key].coalesce()
+            if not numpy.any(numpy.isnan(csg)):
+                globalv.SPECTROGRAMS[key].append(csg)
+                globalv.SPECTROGRAMS[key].coalesce()
+            else:
+                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 48c9109b..680ca47a 100644
--- a/gwsumm/data/spectral.py
+++ b/gwsumm/data/spectral.py
@@ -239,12 +239,17 @@ def _get_spectrogram(channel, segments, config=None, cache=None,
 def add_spectrogram(specgram, key=None, coalesce=True):
     """Add a `Spectrogram` to the global memory cache
     """
-    if key is None:
-        key = specgram.name or str(specgram.channel)
-    globalv.SPECTROGRAMS.setdefault(key, SpectrogramList())
-    globalv.SPECTROGRAMS[key].append(specgram)
-    if coalesce:
-        globalv.SPECTROGRAMS[key].coalesce()
+    if not numpy.any(numpy.isnan(specgram)):
+        if key is None:
+            key = specgram.name or str(specgram.channel)
+        globalv.SPECTROGRAMS.setdefault(key, SpectrogramList())
+        globalv.SPECTROGRAMS[key].append(specgram)
+        if coalesce:
+            globalv.SPECTROGRAMS[key].coalesce()
+    else:
+        warnings.warn('NaN values found in the spectrogram.'
+                      ' Spectrogram will not be appended to'
+                      ' global memory value')
 
 
 @use_segmentlist