diff --git a/include/boost/histogram/algorithm/reduce.hpp b/include/boost/histogram/algorithm/reduce.hpp
index c83181b9..17d80200 100644
--- a/include/boost/histogram/algorithm/reduce.hpp
+++ b/include/boost/histogram/algorithm/reduce.hpp
@@ -11,6 +11,7 @@
 #include <boost/histogram/axis/traits.hpp>
 #include <boost/histogram/detail/axes.hpp>
 #include <boost/histogram/detail/make_default.hpp>
+#include <boost/histogram/detail/reduce_command.hpp>
 #include <boost/histogram/detail/static_if.hpp>
 #include <boost/histogram/fwd.hpp>
 #include <boost/histogram/indexed.hpp>
@@ -23,32 +24,6 @@
 
 namespace boost {
 namespace histogram {
-namespace detail {
-struct reduce_command {
-  static constexpr unsigned unset = static_cast<unsigned>(-1);
-  unsigned iaxis;
-  enum class range_t : char {
-    none,
-    indices,
-    values,
-  } range = range_t::none;
-  union {
-    axis::index_type index;
-    double value;
-  } begin;
-  union {
-    axis::index_type index;
-    double value;
-  } end;
-  unsigned merge = 0; // default value indicates unset option
-  bool crop = false;
-  // for internal use by the reduce algorithm
-  bool is_ordered = true;
-  bool use_underflow_bin = true;
-  bool use_overflow_bin = true;
-};
-} // namespace detail
-
 namespace algorithm {
 
 /** Holder for a reduce command.
diff --git a/include/boost/histogram/detail/reduce_command.hpp b/include/boost/histogram/detail/reduce_command.hpp
new file mode 100644
index 00000000..a3262fe4
--- /dev/null
+++ b/include/boost/histogram/detail/reduce_command.hpp
@@ -0,0 +1,40 @@
+// Copyright 2020 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_DETAIL_REDUCE_COMMAND_HPP
+#define BOOST_HISTOGRAM_DETAIL_REDUCE_COMMAND_HPP
+
+#include <boost/histogram/fwd.hpp>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+
+struct reduce_command {
+  static constexpr unsigned unset = static_cast<unsigned>(-1);
+  unsigned iaxis;
+  enum class range_t : char {
+    none,
+    indices,
+    values,
+  } range = range_t::none;
+  union {
+    axis::index_type index;
+    double value;
+  } begin, end;
+  unsigned merge = 0; // default value indicates unset option
+  bool crop = false;
+  // for internal use by the reduce algorithm
+  bool is_ordered = true;
+  bool use_underflow_bin = true;
+  bool use_overflow_bin = true;
+};
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif