diff --git a/loopy/codegen/expression.py b/loopy/codegen/expression.py
index 54bb64f488da13e2123ed9a0268dfd7ef50d4efd..a270944016c9c69163be5a94df7e9fc7cfbd4feb 100644
--- a/loopy/codegen/expression.py
+++ b/loopy/codegen/expression.py
@@ -85,6 +85,9 @@ class TypeInferenceMapper(CombineMapper):
         dtype, offset = agg_result.fields[expr.name]
         return dtype
 
+    def map_reduction(self, expr):
+        return expr.operation.dtype(expr.inames)
+
 # }}}
 
 # {{{ C code mapper