diff --git a/artiq/py2llvm/ast_body.py b/artiq/py2llvm/ast_body.py
index 306ffb821..3cba3a976 100644
--- a/artiq/py2llvm/ast_body.py
+++ b/artiq/py2llvm/ast_body.py
@@ -200,7 +200,7 @@ class Visitor:
             for elt in elts[1:]:
                 el_type.merge(elt)
         else:
-            el_type = VNone()
+            el_type = base_types.VNone()
         count = len(elts)
         r = lists.VList(el_type, count)
         r.elts = elts
diff --git a/artiq/py2llvm/lists.py b/artiq/py2llvm/lists.py
index 14e59622d..ded97773e 100644
--- a/artiq/py2llvm/lists.py
+++ b/artiq/py2llvm/lists.py
@@ -30,7 +30,14 @@ class VList(VGeneric):
 
     def merge(self, other):
         if isinstance(other, VList):
-            self.el_type.merge(other.el_type)
+            if self.alloc_count:
+                if other.alloc_count:
+                    self.el_type.merge(other.el_type)
+                    if self.alloc_count < other.alloc_count:
+                        self.alloc_count = other.alloc_count
+            else:
+                self.el_type = other.el_type.new()
+                self.alloc_count = other.alloc_count
         else:
             raise TypeError("Incompatible types: {} and {}"
                             .format(repr(self), repr(other)))