diff --git a/loopy/__init__.py b/loopy/__init__.py
index 3c43339a48c65cd4193efd754fc639e109a2af01..a90e99ffd1d9123f7940753c86f24843e951ddd0 100644
--- a/loopy/__init__.py
+++ b/loopy/__init__.py
@@ -230,7 +230,8 @@ def realize_cse(kernel, cse_tag, dtype, duplicate_inames=[], parallel_inames=Non
         forced_iname_deps = []
 
         from loopy.symbolic import IndexVariableFinder
-        dependencies = IndexVariableFinder()(expr.child)
+        dependencies = IndexVariableFinder(
+                include_reduction_inames=False)(expr.child)
 
         assert dependencies <= parent_inames
 
diff --git a/loopy/kernel.py b/loopy/kernel.py
index ffbae5657e650b1894a99695899546169c7decb1..f047f90cc9dfc3c00ea8faa52217355f9bbdd583 100644
--- a/loopy/kernel.py
+++ b/loopy/kernel.py
@@ -236,9 +236,8 @@ class Instruction(Record):
     @memoize_method
     def all_inames(self):
         from loopy.symbolic import IndexVariableFinder
-        index_vars = (
-                IndexVariableFinder()(self.expression)
-                | IndexVariableFinder()(self.assignee))
+        ivarf = IndexVariableFinder(include_reduction_inames=False)
+        index_vars = (ivarf(self.expression) | ivarf(self.assignee))
 
         return index_vars | set(self.forced_iname_deps)
 
diff --git a/loopy/symbolic.py b/loopy/symbolic.py
index 4504daa7d21f63749d02e8fbd9c4cd139fe372c0..25667eaa1bb0e6d6fc424941366b8441b1ddc927 100644
--- a/loopy/symbolic.py
+++ b/loopy/symbolic.py
@@ -485,6 +485,9 @@ class ReductionCallbackMapper(IdentityMapper):
 # {{{ index dependency finding
 
 class IndexVariableFinder(CombineMapper):
+    def __init__(self, include_reduction_inames):
+        self.include_reduction_inames = include_reduction_inames
+
     def combine(self, values):
         import operator
         return reduce(operator.or_, values, set())
@@ -508,7 +511,14 @@ class IndexVariableFinder(CombineMapper):
         return result
 
     def map_reduction(self, expr):
-        return set(expr.inames) | self.rec(expr.expr)
+        result = self.rec(expr.expr)
+        if not set(expr.inames) <= result:
+            raise RuntimeError("reduction '%s' does not depend on "
+                    "reduction inames" % expr)
+        if self.include_reduction_inames:
+            return result
+        else:
+            return result - set(expr.inames)
 
 # }}}