diff --git a/src/etc/etc.py b/src/etc/etc.py
index a73e070..69ef3ef 100644
--- a/src/etc/etc.py
+++ b/src/etc/etc.py
@@ -162,7 +162,8 @@ def photons_from_source(
         standard_filter = self._convert_filtername(filtername)
         band = self._map_filter_to_standard(mag_filter)
         print(band.meta.get("expr", "Unknown"), type(source_spec))
-        source_spec = source_spec or self._vega
+        if source_spec is None:
+            source_spec = self._vega
         if type(source_spec) != SourceSpectrum:
             raise ETCError("Invalid sourcespec; must be a SourceSpectrum")