diff --git a/loopy/__init__.py b/loopy/__init__.py
index ad008f943499e721c8250d3f163d5317a000d453..47df9b0d00f2cebb6d9ffcf05085ce33c7f87ba4 100644
--- a/loopy/__init__.py
+++ b/loopy/__init__.py
@@ -320,10 +320,10 @@ def make_slab(space, iname, start, stop):
     from pymbolic import var
     var_iname = var(iname)
     return (isl.Set.universe(space)
-            # 0 <= inner
+            # start <= inner
             .add_constraint(ineq_constraint_from_expr(
-                space, start + var_iname))
-            # inner < length
+                space, var_iname -start))
+            # inner < stop
             .add_constraint(ineq_constraint_from_expr(
                 space, stop-1 - var_iname)))