diff --git a/common/main/player-callsign.h b/common/main/player-callsign.h
index f619cc2a8..127118cb9 100644
--- a/common/main/player-callsign.h
+++ b/common/main/player-callsign.h
@@ -41,10 +41,13 @@ struct callsign_t
 		a = {};
 		std::copy_n(s.data(), std::min(a.size() - 1, s.size()), begin(a));
 	}
-	void copy_lower(const char *s, std::size_t N)
+	template <std::size_t Extent>
+		requires(Extent == std::dynamic_extent || Extent <= array_length)
+	void copy_lower(const std::span<const char, Extent> sc)
 	{
 		a = {};
-		std::transform(s, std::next(s, std::min(a.size() - 1, N)), begin(a), lower_predicate);
+		const auto s = sc.data();
+		std::transform(s, std::next(s, std::min(a.size() - 1, sc.size())), begin(a), lower_predicate);
 	}
 	void lower()
 	{
@@ -62,12 +65,6 @@ struct callsign_t
 		{
 			copy(std::span(s));
 		}
-	template <std::size_t N>
-		void copy_lower(const char (&s)[N])
-		{
-			static_assert(N <= array_length, "string too long");
-			copy_lower(s, N);
-		}
 	void fill(char c) { a.fill(c); }
 	const char &operator[](std::size_t i) const
 	{
diff --git a/similar/main/config.cpp b/similar/main/config.cpp
index c2aa2a957..d5e9c673b 100644
--- a/similar/main/config.cpp
+++ b/similar/main/config.cpp
@@ -197,7 +197,7 @@ int ReadConfigFile()
 			gr_palette_set_gamma(CGameCfg.GammaLevel);
 		}
 		else if (cmp(lb, eq, LastPlayerStr))
-			GameCfg.LastPlayer.copy_lower(value, std::distance(value, eol));
+			GameCfg.LastPlayer.copy_lower(std::span(value, std::distance(value, eol)));
 		else if (cmp(lb, eq, LastMissionStr))
 			convert_string(CGameCfg.LastMission, value, eol);
 		else if (cmp(lb, eq, ResolutionXStr))
diff --git a/similar/main/menu.cpp b/similar/main/menu.cpp
index b3c6fd460..a7f85b2b3 100644
--- a/similar/main/menu.cpp
+++ b/similar/main/menu.cpp
@@ -533,7 +533,7 @@ window_event_result pilot_selection_listbox::callback_handler(const d_event &eve
 			else
 			{
 				const auto p = item[citem];
-				InterfaceUniqueState.PilotName.copy_lower(p, strlen(p));
+				InterfaceUniqueState.PilotName.copy_lower(std::span(p, strlen(p)));
 				InterfaceUniqueState.update_window_title();
 			}
 			return window_event_result::close;
diff --git a/similar/main/net_udp.cpp b/similar/main/net_udp.cpp
index 5fc675cde..0fc137f89 100644
--- a/similar/main/net_udp.cpp
+++ b/similar/main/net_udp.cpp
@@ -1750,7 +1750,7 @@ static auto build_udp_sequence_from_untrusted(const std::span<const uint8_t, upi
 	callsign_t callsign;
 	/* Skip over the first byte, since it is the UPID code */
 	std::size_t position = 1;
-	callsign.copy_lower(reinterpret_cast<const char *>(&untrusted[position]), CALLSIGN_LEN);
+	callsign.copy_lower(std::span<const char, CALLSIGN_LEN>(reinterpret_cast<const char *>(&untrusted[position]), CALLSIGN_LEN));
 	position += CALLSIGN_LEN + 1;
 	const netplayer_info::player_rank rank = build_rank_from_untrusted(untrusted[++position]);
 	return std::tuple(callsign, rank);
@@ -3176,7 +3176,7 @@ static void net_udp_process_game_info_heavy(const uint8_t *data, uint_fast32_t,
 		Netgame.protocol.udp.your_index = data[len]; ++len;
 		range_for (auto &i, Netgame.players)
 		{
-			i.callsign.copy_lower(reinterpret_cast<const char *>(&data[len]), CALLSIGN_LEN);
+			i.callsign.copy_lower(std::span<const char, CALLSIGN_LEN>(reinterpret_cast<const char *>(&data[len]), CALLSIGN_LEN));
 			len += CALLSIGN_LEN+1;
 			i.connected = player_connection_status{data[len]};				len++;
 			i.rank = build_rank_from_untrusted(data[len]);					len++;