diff --git a/README.md b/README.md
index c91a52e..c4459f6 100644
--- a/README.md
+++ b/README.md
@@ -141,9 +141,9 @@ enum class Color { RED = 2, BLUE = 4, GREEN = 8 };
 * Enum fusion for multi-level switch/case statements
 
   ```cpp
-  switch (magic_enum::enum_fuse(color1, color2)) {
-  case magic_enum::enum_fuse(RED, BLUE): // ...
-  case magic_enum::enum_fuse(RED, RED):  // ...
+  switch (magic_enum::enum_fuse(color, direction)) {
+    case magic_enum::enum_fuse(Color::RED, Directions::Up): // ...
+    case magic_enum::enum_fuse(Color::BLUE, Directions::Down): // ...
   // ...
   }
   ```
diff --git a/doc/reference.md b/doc/reference.md
index 7e4094d..867e347 100644
--- a/doc/reference.md
+++ b/doc/reference.md
@@ -329,8 +329,8 @@ constexpr string_view enum_type_name() noexcept;
 ## `enum_fuse`
 
 ```cpp
-template<typename ... Es>
-[[nodiscard]] constexpr size_t enum_fuse(Es ... values);
+template <typename... Es>
+[[nodiscard]] constexpr std::size_t enum_fuse(Es... values);
 ```
 
 * Returns a bijective mix of several enum values with [Cantor pairing function](https://en.wikipedia.org/wiki/Pairing_function). This can be used to emulate 2D switch/case statements.
@@ -338,9 +338,9 @@ template<typename ... Es>
 * Examples
 
   ```cpp
-  switch (magic_enum::enum_fuse(color1, color2)) {
-  case magic_enum::enum_fuse(RED, BLUE): // ...
-  case magic_enum::enum_fuse(RED, RED):  // ...
+  switch (magic_enum::enum_fuse(color, direction)) {
+    case magic_enum::enum_fuse(Color::RED, Directions::Up): // ...
+    case magic_enum::enum_fuse(Color::BLUE, Directions::Down): // ...
   // ...
   }
   ```
diff --git a/include/magic_enum.hpp b/include/magic_enum.hpp
index bb63bac..6ac75ee 100644
--- a/include/magic_enum.hpp
+++ b/include/magic_enum.hpp
@@ -324,6 +324,15 @@ constexpr I log2(I value) noexcept {
   return ret;
 }
 
+constexpr std::size_t cantor_pair(size_t v1, size_t v2) noexcept {
+  return (((v1 + v2) * (v1 + v2 + 1)) >> 1) + v2;
+}
+
+template <typename... Ts>
+constexpr std::size_t cantor_pair(std::size_t v1, std::size_t head, Ts... tail) noexcept {
+  return cantor_pair(cantor_pair(v1, head), tail...);
+}
+
 template <typename T>
 inline constexpr bool is_enum_v = std::is_enum_v<T> && std::is_same_v<T, std::decay_t<T>>;
 
@@ -609,15 +618,6 @@ struct underlying_type {};
 template <typename T>
 struct underlying_type<T, true> : std::underlying_type<std::decay_t<T>> {};
 
-constexpr size_t cantor_pair(size_t v1, size_t v2) noexcept {
-  return (((v1 + v2) * (v1 + v2 + 1)) >> 1) + v2;
-}
-
-template<typename ... Ts>
-constexpr size_t cantor_pair(size_t v1, size_t head, Ts ... tail) noexcept {
-  return cantor_pair(cantor_pair(v1, head), tail...);
-}
-
 } // namespace magic_enum::detail
 
 // Checks is magic_enum supported compiler.
@@ -887,11 +887,17 @@ template <typename E>
   return {}; // Invalid value or out of range.
 }
 
-template<typename ... Es>
-[[nodiscard]] constexpr size_t enum_fuse(Es ... enums) {
+// Returns a bijective mix of several enum values with [Cantor pairing function](https://en.wikipedia.org/wiki/Pairing_function). This can be used to emulate 2D switch/case statements.
+template <typename... Es>
+[[nodiscard]] constexpr auto enum_fuse(Es... values) -> std::enable_if_t<(std::is_enum_v<std::decay_t<Es>> && ...), std::size_t>{
   static_assert(sizeof...(Es) >= 2, "magic_enum::enum_fuse requires at least 2 enums");
+#ifdef __cpp_lib_is_constant_evaluated
+  if (std::is_constant_evaluated() && !(enum_index(values).has_value() && ...)) {
+    throw std::logic_error("magic_enum::enum_fuse accepts only in-range enum values");
+  }
+#endif
   // Add 1 to prevent matching 2D fusions with 3D fusions etc.
-  return detail::cantor_pair((enum_index(enums).value() + 1)...);
+  return assert((enum_index(values).has_value() && ...)), detail::cantor_pair((enum_index(values).value() + 1)...);
 }
 
 // Checks whether enum contains enumerator with such enum value.
diff --git a/test/test.cpp b/test/test.cpp
index 3540924..348ff30 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -1014,32 +1014,28 @@ TEST_CASE("constexpr_for") {
   });
 }
 
-static int switch_case_2d(Color color, Directions number)
-{
-  switch (magic_enum::enum_fuse(color, number))
-  {
-  case magic_enum::enum_fuse(Color::RED, Directions::Up):
-    return 1;
-  case magic_enum::enum_fuse(Color::BLUE, Directions::Down):
-    return 2;
-  default:
-    return 0;
+static int switch_case_2d(Color color, Directions direction) {
+  switch (magic_enum::enum_fuse(color, direction)) {
+    case magic_enum::enum_fuse(Color::RED, Directions::Up):
+      return 1;
+    case magic_enum::enum_fuse(Color::BLUE, Directions::Down):
+      return 2;
+    default:
+      return 0;
   }
 }
 
 enum class Index { zero = 0, one = 1, two = 2 };
 
-static int switch_case_3d(Color color, Directions number, Index index)
-{
-  switch (magic_enum::enum_fuse(color, number, index))
-  {
-  case magic_enum::enum_fuse(Color::RED, Directions::Up, Index::zero):
-    return 1;
-  // model accidental removal of last index, must not match anything
-  case magic_enum::enum_fuse(Color::BLUE, Directions::Up):
-    return 2;
-  default:
-    return 0;
+static int switch_case_3d(Color color, Directions direction, Index index) {
+  switch (magic_enum::enum_fuse(color, direction, index)) {
+    case magic_enum::enum_fuse(Color::RED, Directions::Up, Index::zero):
+      return 1;
+    // model accidental removal of last index, must not match anything
+    case magic_enum::enum_fuse(Color::BLUE, Directions::Up):
+      return 2;
+    default:
+      return 0;
   }
 }