diff --git a/lslopt/lslfoldconst.py b/lslopt/lslfoldconst.py
index 6353083..1c10f66 100644
--- a/lslopt/lslfoldconst.py
+++ b/lslopt/lslfoldconst.py
@@ -238,7 +238,7 @@ class foldconst(object):
         if nt == 'FNCALL':
             sym = self.symtab[0][node['name']]
             if sym['Type'] == 'integer' and 'min' in sym and 'max' in sym \
-               and sym['min'] == 0 and sym['max'] == 1:
+               and sym['min'] >= 0 and sym['max'] <= 1:
                 return True
 
         return False