diff --git a/common/main/cast_range_result.h b/common/main/cast_range_result.h
index 4c0c079d2..038b75111 100644
--- a/common/main/cast_range_result.h
+++ b/common/main/cast_range_result.h
@@ -11,9 +11,28 @@
 #include "partial_range.h"
 
 template <typename result_type, typename iterator_type>
+/* Declare the requirements on the class itself, rather than the one method which needs them, because:
+ * - the class is useless if that one method fails its requirements
+ * - gcc produces better error messages if the class is rejected, than if the
+ *   class is accepted and `operator*()` is rejected.
+ */
+requires(
+	requires(iterator_type i) {
+		/* If the base type's result cannot be converted to this type's result,
+		 * then `operator*()` will raise an error when it attempts an implicit
+		 * conversion.
+		 */
+		{*i} -> std::convertible_to<result_type>;
+		/* If `result_type` and the base type's `operator*` are the same, then
+		 * this adapter has no effect.
+		 */
+		requires(!std::is_same<result_type, decltype(*i)>::value);
+	}
+)
 class iterator_result_converter : public iterator_type
 {
 public:
+	constexpr iterator_result_converter() = default;
 	iterator_result_converter(iterator_type &&iter) :
 		iterator_type(std::move(iter))
 	{
@@ -22,6 +41,10 @@ public:
 	{
 		return *this;
 	}
+	/* `using iterator_type::operator*()` is not viable here because this
+	 * `operator*()` has a different return type than
+	 * `iterator_type::operator*()`.
+	 */
 	result_type operator*() const
 	{
 		return this->iterator_type::operator*();
@@ -30,6 +53,12 @@ public:
 	{
 		return static_cast<iterator_result_converter &>(this->iterator_type::operator++());
 	}
+	iterator_result_converter operator++(int)
+	{
+		auto r = *this;
+		this->iterator_type::operator++();
+		return r;
+	}
 };
 
 template <typename result_type, typename range_type, typename iterator_type = iterator_result_converter<result_type, decltype(std::begin(std::declval<range_type &>()))>>