diff --git a/src/pysme/sme_synth.py b/src/pysme/sme_synth.py
index df31ecde..cb9edb29 100644
--- a/src/pysme/sme_synth.py
+++ b/src/pysme/sme_synth.py
@@ -244,6 +244,8 @@ def InputAbund(self, abund):
             abundance structure to be passed (see Abund for more details)
         """
         abund = abund("sme", raw=True)
+        # TODO: does this make sense or should we fix the C code?
+        abund[np.isnan(abund)] = -12
         _smelib.InputAbund(abund)
 
     def Opacity(self):