diff --git a/avogadro/core/spacegroups.cpp b/avogadro/core/spacegroups.cpp
index d96b239a6..4448fbfb2 100644
--- a/avogadro/core/spacegroups.cpp
+++ b/avogadro/core/spacegroups.cpp
@@ -27,7 +27,7 @@ SpaceGroups::~SpaceGroups() {}
 unsigned short SpaceGroups::hallNumber(const std::string& spaceGroup)
 {
   unsigned short hall = 0; // can't find anything
-  const unsigned short hall_count = 530;
+  const unsigned short hall_count = 531; // 530 but first one is empty
   // some files use " instead of = for the space group symbol
   std::string sg = spaceGroup;
   std::replace(sg.begin(), sg.end(), '"', '=');