diff --git a/NEWS b/NEWS
index 19df7e53e..da37166ec 100644
--- a/NEWS
+++ b/NEWS
@@ -54,6 +54,7 @@ ver 0.21.26 (not yet released)
 * decoder
   - ffmpeg: remove "rtsp://" from the list of supported protocols
   - ffmpeg: add "hls+http://" to the list of supported protocols
+  - opus: support the gain value from the Opus header
   - sndfile: fix lost samples at end of file
 * fix "single" mode bug after resuming playback
 * the default log_level is "default", not "info"
diff --git a/src/decoder/plugins/OpusDecoderPlugin.cxx b/src/decoder/plugins/OpusDecoderPlugin.cxx
index ba5a2bff4..a0cf02ba7 100644
--- a/src/decoder/plugins/OpusDecoderPlugin.cxx
+++ b/src/decoder/plugins/OpusDecoderPlugin.cxx
@@ -75,6 +75,12 @@ class MPDOpusDecoder final : public OggDecoder {
 	OpusDecoder *opus_decoder = nullptr;
 	opus_int16 *output_buffer = nullptr;
 
+	/**
+	 * The output gain from the Opus header. Initialized by
+	 * OnOggBeginning().
+	 */
+	signed output_gain;
+
 	/**
 	 * The pre-skip value from the Opus header.  Initialized by
 	 * OnOggBeginning().
@@ -164,7 +170,7 @@ MPDOpusDecoder::OnOggBeginning(const ogg_packet &packet)
 		throw std::runtime_error("BOS packet must be OpusHead");
 
 	unsigned channels;
-	if (!ScanOpusHeader(packet.packet, packet.bytes, channels, pre_skip) ||
+	if (!ScanOpusHeader(packet.packet, packet.bytes, channels, output_gain, pre_skip) ||
 	    !audio_valid_channel_count(channels))
 		throw std::runtime_error("Malformed BOS packet");
 
@@ -239,6 +245,15 @@ MPDOpusDecoder::HandleTags(const ogg_packet &packet)
 	ReplayGainInfo rgi;
 	rgi.Clear();
 
+	/**
+	 * Output gain is a Q7.8 fixed point number in dB that should be,
+	 * applied unconditionally, but is often used specifically for
+	 * ReplayGain. Add 5dB to compensate for the different
+	 * reference levels between ReplayGain (89dB) and EBU R128 (-23 LUFS).
+	 */
+	rgi.track.gain = float(output_gain) / 256.0f + 5;
+	rgi.album.gain = float(output_gain) / 256.0f + 5;
+
 	TagBuilder tag_builder;
 	AddTagHandler h(tag_builder);
 
@@ -384,14 +399,14 @@ mpd_opus_stream_decode(DecoderClient &client,
 
 bool
 ReadAndParseOpusHead(OggSyncState &sync, OggStreamState &stream,
-		     unsigned &channels, unsigned &pre_skip)
+		     unsigned &channels, signed &output_gain, unsigned &pre_skip)
 {
 	ogg_packet packet;
 
 	return OggReadPacket(sync, stream, packet) && packet.b_o_s &&
 		IsOpusHead(packet) &&
 		ScanOpusHeader(packet.packet, packet.bytes, channels,
-			       pre_skip) &&
+			       output_gain, pre_skip) &&
 		audio_valid_channel_count(channels);
 }
 
@@ -436,7 +451,8 @@ mpd_opus_scan_stream(InputStream &is, TagHandler &handler)
 	OggStreamState os(first_page);
 
 	unsigned channels, pre_skip;
-	if (!ReadAndParseOpusHead(oy, os, channels, pre_skip) ||
+	signed output_gain;
+	if (!ReadAndParseOpusHead(oy, os, channels, output_gain, pre_skip) ||
 	    !ReadAndVisitOpusTags(oy, os, handler))
 		return false;
 
diff --git a/src/decoder/plugins/OpusHead.cxx b/src/decoder/plugins/OpusHead.cxx
index 596ef186a..eb7edf121 100644
--- a/src/decoder/plugins/OpusHead.cxx
+++ b/src/decoder/plugins/OpusHead.cxx
@@ -33,12 +33,14 @@ struct OpusHead {
 
 bool
 ScanOpusHeader(const void *data, size_t size, unsigned &channels_r,
-	       unsigned &pre_skip_r)
+	       signed &output_gain_r, unsigned &pre_skip_r)
 {
 	const auto *h = (const OpusHead *)data;
 	if (size < 19 || (h->version & 0xf0) != 0)
 		return false;
 
+	output_gain_r = FromLE16S(h->output_gain);
+
 	channels_r = h->channels;
 	pre_skip_r = FromLE16(h->pre_skip);
 	return true;
diff --git a/src/decoder/plugins/OpusHead.hxx b/src/decoder/plugins/OpusHead.hxx
index d140cee21..cbacf0c48 100644
--- a/src/decoder/plugins/OpusHead.hxx
+++ b/src/decoder/plugins/OpusHead.hxx
@@ -24,6 +24,6 @@
 
 bool
 ScanOpusHeader(const void *data, size_t size, unsigned &channels_r,
-	       unsigned &pre_skip_r);
+	       signed &output_gain_r, unsigned &pre_skip_r);
 
 #endif
diff --git a/src/decoder/plugins/OpusTags.cxx b/src/decoder/plugins/OpusTags.cxx
index ee1d0cb22..c78586065 100644
--- a/src/decoder/plugins/OpusTags.cxx
+++ b/src/decoder/plugins/OpusTags.cxx
@@ -61,7 +61,7 @@ ScanOneOpusTag(StringView name, StringView value,
 		const char *endptr;
 		const auto l = ParseInt64(value, &endptr, 10);
 		if (endptr > value.begin() && endptr == value.end())
-			rgi->track.gain = float(l) / 256.0f;
+			rgi->track.gain += float(l) / 256.0f;
 	} else if (rgi != nullptr &&
 		   name.EqualsIgnoreCase("R128_ALBUM_GAIN")) {
 		/* R128_ALBUM_GAIN is a Q7.8 fixed point number in
@@ -70,7 +70,7 @@ ScanOneOpusTag(StringView name, StringView value,
 		const char *endptr;
 		const auto l = ParseInt64(value, &endptr, 10);
 		if (endptr > value.begin() && endptr == value.end())
-			rgi->album.gain = float(l) / 256.0f;
+			rgi->album.gain += float(l) / 256.0f;
 	}
 
 	handler.OnPair(name, value);
diff --git a/src/pcm/Mix.cxx b/src/pcm/Mix.cxx
index ed2b0f8db..9126f60f6 100644
--- a/src/pcm/Mix.cxx
+++ b/src/pcm/Mix.cxx
@@ -27,6 +27,7 @@
 #include "Dither.cxx" // including the .cxx file to get inlined templates
 
 #include <cassert>
+#include <cmath>
 
 template<SampleFormat F, class Traits=SampleTraits<F>>
 static typename Traits::value_type
diff --git a/src/util/ByteOrder.hxx b/src/util/ByteOrder.hxx
index 2c145a262..48222854e 100644
--- a/src/util/ByteOrder.hxx
+++ b/src/util/ByteOrder.hxx
@@ -243,4 +243,15 @@ ToLE64(uint64_t value) noexcept
 	return IsLittleEndian() ? value : ByteSwap64(value);
 }
 
+/**
+ * Converts a 16 bit integer from little endian to the host byte order
+ * and returns it as a signed integer.
+ */
+constexpr int16_t
+FromLE16S(uint16_t value) noexcept
+{
+	/* assuming two's complement representation */
+	return static_cast<int16_t>(FromLE16(value));
+}
+
 #endif