diff --git a/src/command/CommandError.cxx b/src/command/CommandError.cxx
index 149f0a0ab..345eb6fec 100644
--- a/src/command/CommandError.cxx
+++ b/src/command/CommandError.cxx
@@ -27,8 +27,7 @@
 
 #include <system_error>
 
-gcc_const
-static enum ack
+static constexpr enum ack
 ToAck(PlaylistResult result) noexcept
 {
 	switch (result) {
@@ -63,8 +62,8 @@ ToAck(PlaylistResult result) noexcept
 }
 
 #ifdef ENABLE_DATABASE
-gcc_const
-static enum ack
+
+static constexpr enum ack
 ToAck(DatabaseErrorCode code) noexcept
 {
 	switch (code) {
@@ -78,9 +77,10 @@ ToAck(DatabaseErrorCode code) noexcept
 
 	return ACK_ERROR_UNKNOWN;
 }
+
 #endif
 
-gcc_pure
+[[gnu::pure]]
 static enum ack
 ToAck(const std::exception_ptr& ep) noexcept
 {
diff --git a/src/db/update/InotifyQueue.cxx b/src/db/update/InotifyQueue.cxx
index 1e4fa00e5..b731faa61 100644
--- a/src/db/update/InotifyQueue.cxx
+++ b/src/db/update/InotifyQueue.cxx
@@ -69,7 +69,7 @@ InotifyQueue::OnDelay() noexcept
 	}
 }
 
-gcc_pure
+[[gnu::pure]]
 static bool
 path_in(const char *path, const char *possible_parent) noexcept
 {
diff --git a/src/lib/ffmpeg/LogCallback.cxx b/src/lib/ffmpeg/LogCallback.cxx
index baf5ec687..d62c0e38c 100644
--- a/src/lib/ffmpeg/LogCallback.cxx
+++ b/src/lib/ffmpeg/LogCallback.cxx
@@ -30,7 +30,7 @@ extern "C" {
 #include <libavutil/log.h>
 }
 
-gcc_const
+[[gnu::const]]
 static LogLevel
 FfmpegImportLogLevel(int level) noexcept
 {
diff --git a/src/lib/upnp/Discovery.cxx b/src/lib/upnp/Discovery.cxx
index e7c2c8569..1cc8f813a 100644
--- a/src/lib/upnp/Discovery.cxx
+++ b/src/lib/upnp/Discovery.cxx
@@ -99,7 +99,7 @@ static constexpr char ContentDirectorySType[] = "urn:schemas-upnp-org:service:Co
 
 // We don't include a version in comparisons, as we are satisfied with
 // version 1
-gcc_pure
+[[gnu::pure]]
 static bool
 isCDService(const char *st) noexcept
 {
@@ -110,7 +110,7 @@ isCDService(const char *st) noexcept
 // The type of device we're asking for in search
 static constexpr char MediaServerDType[] = "urn:schemas-upnp-org:device:MediaServer:1";
 
-gcc_pure
+[[gnu::pure]]
 static bool
 isMSDevice(const char *st) noexcept
 {
diff --git a/src/neighbor/plugins/UpnpNeighborPlugin.cxx b/src/neighbor/plugins/UpnpNeighborPlugin.cxx
index 821ece602..e0bcbf615 100644
--- a/src/neighbor/plugins/UpnpNeighborPlugin.cxx
+++ b/src/neighbor/plugins/UpnpNeighborPlugin.cxx
@@ -40,12 +40,12 @@ class UpnpNeighborExplorer final
 		Server(const Server &) = delete;
 		Server &operator=(const Server &) = delete;
 
-		gcc_pure
+		[[gnu::pure]]
 		bool operator==(const Server &other) const noexcept {
 			return name == other.name;
 		}
 
-		[[nodiscard]] gcc_pure
+		[[nodiscard]] [[gnu::pure]]
 		NeighborInfo Export() const noexcept {
 			return { "smb://" + name + "/", comment };
 		}