diff --git a/loopy/codegen/expression.py b/loopy/codegen/expression.py
index 964d7efc1f6d681f618d0fc7edfc3314cdef4a56..da323a79444e8a3b1d28beb7f19776e3e2db0e9d 100644
--- a/loopy/codegen/expression.py
+++ b/loopy/codegen/expression.py
@@ -310,9 +310,13 @@ class LoopyCCodeMapper(RecursiveMapper):
             raise RuntimeError("nothing known about variable '%s'" % expr.aggregate.name)
 
     def map_floor_div(self, expr, enclosing_prec, type_context):
+        from loopy.symbolic import get_dependencies
+        iname_deps = get_dependencies(expr) & self.kernel.all_inames()
+        domain = self.kernel.get_inames_domain(iname_deps)
+
         from loopy.isl_helpers import is_nonnegative
-        num_nonneg = is_nonnegative(expr.numerator, self.kernel.domain)
-        den_nonneg = is_nonnegative(expr.denominator, self.kernel.domain)
+        num_nonneg = is_nonnegative(expr.numerator, domain)
+        den_nonneg = is_nonnegative(expr.denominator, domain)
 
         if den_nonneg:
             if num_nonneg: