diff --git a/src/util/CopyConst.hxx b/src/util/CopyConst.hxx
new file mode 100644
index 000000000..3d38b8d24
--- /dev/null
+++ b/src/util/CopyConst.hxx
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2022 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <type_traits>
+
+/**
+ * Generate a type based on #To with the same const-ness as #From.
+ */
+template<typename To, typename From>
+using CopyConst = std::conditional_t<std::is_const_v<From>,
+				     const To,
+				     To>;
diff --git a/src/util/SpanCast.hxx b/src/util/SpanCast.hxx
index e5b927cd5..11f5b60ce 100644
--- a/src/util/SpanCast.hxx
+++ b/src/util/SpanCast.hxx
@@ -29,14 +29,13 @@
 
 #pragma once
 
+#include "CopyConst.hxx"
+
 #include <cassert>
 #include <cstddef>
 #include <span>
 #include <string_view>
 
-template<typename To, typename From>
-using CopyConst = std::conditional_t<std::is_const_v<From>, const To, To>;
-
 /**
  * Cast a std::span<std::byte> to a std::span<T>, rounding down to the
  * next multiple of T's size.