diff --git a/src/music/fluidsynth.cpp b/src/music/fluidsynth.cpp
--- a/src/music/fluidsynth.cpp
+++ b/src/music/fluidsynth.cpp
@@ -15,11 +15,13 @@
 #include "midifile.hpp"
 #include <fluidsynth.h>
 #include "../mixer.h"
+#include <mutex>
 
 static struct {
 	fluid_settings_t* settings;    ///< FluidSynth settings handle
 	fluid_synth_t* synth;          ///< FluidSynth synthesizer handle
 	fluid_player_t* player;        ///< FluidSynth MIDI player handle
+	std::mutex synth_mutex;        ///< Guard mutex for synth access
 } _midi; ///< Metadata about the midi we're playing.
 
 /** Factory for the FluidSynth driver. */
@@ -42,12 +44,16 @@ static const char *default_sf[] = {
 
 static void RenderMusicStream(int16 *buffer, size_t samples)
 {
-	if (!_midi.synth || !_midi.player) return;
+	std::unique_lock<std::mutex> lock{ _midi.synth_mutex, std::try_to_lock };
+
+	if (!lock.owns_lock() || !_midi.synth || !_midi.player) return;
 	fluid_synth_write_s16(_midi.synth, samples, buffer, 0, 2, buffer, 1, 2);
 }
 
 const char *MusicDriver_FluidSynth::Start(const char * const *param)
 {
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
+
 	const char *sfont_name = GetDriverParam(param, "soundfont");
 	int sfont_id;
 
@@ -59,6 +65,11 @@ const char *MusicDriver_FluidSynth::Star
 	/* Don't try to lock sample data in memory, OTTD usually does not run with privileges allowing that */
 	fluid_settings_setint(_midi.settings, "synth.lock-memory", 0);
 
+	/* Install the music render routine and set up the samplerate */
+	uint32 samplerate = MxSetMusicSource(RenderMusicStream);
+	fluid_settings_setnum(_midi.settings, "synth.sample-rate", samplerate);
+	DEBUG(driver, 1, "Fluidsynth: samplerate %.0f", (float)samplerate);
+
 	/* Create the synthesizer. */
 	_midi.synth = new_fluid_synth(_midi.settings);
 	if (!_midi.synth) return "Could not open synth";
@@ -81,19 +92,23 @@ const char *MusicDriver_FluidSynth::Star
 
 	_midi.player = nullptr;
 
-	uint32 samplerate = MxSetMusicSource(RenderMusicStream);
-	fluid_synth_set_sample_rate(_midi.synth, samplerate);
-	DEBUG(driver, 1, "Fluidsynth: samplerate %.0f", (float)samplerate);
-
 	return nullptr;
 }
 
 void MusicDriver_FluidSynth::Stop()
 {
 	MxSetMusicSource(nullptr);
-	this->StopSong();
-	delete_fluid_synth(_midi.synth);
-	delete_fluid_settings(_midi.settings);
+
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
+
+	if (_midi.player != nullptr) delete_fluid_player(_midi.player);
+	_midi.player = nullptr;
+
+	if (_midi.synth != nullptr) delete_fluid_synth(_midi.synth);
+	_midi.synth = nullptr;
+
+	if (_midi.settings != nullptr) delete_fluid_settings(_midi.settings);
+	_midi.settings = nullptr;
 }
 
 void MusicDriver_FluidSynth::PlaySong(const MusicSongInfo &song)
@@ -106,6 +121,8 @@ void MusicDriver_FluidSynth::PlaySong(co
 		return;
 	}
 
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
+
 	_midi.player = new_fluid_player(_midi.synth);
 	if (!_midi.player) {
 		DEBUG(driver, 0, "Could not create midi player");
@@ -128,6 +145,8 @@ void MusicDriver_FluidSynth::PlaySong(co
 
 void MusicDriver_FluidSynth::StopSong()
 {
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
+
 	if (!_midi.player) return;
 
 	fluid_player_stop(_midi.player);
@@ -142,6 +161,7 @@ void MusicDriver_FluidSynth::StopSong()
 
 bool MusicDriver_FluidSynth::IsSongPlaying()
 {
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
 	if (!_midi.player) return false;
 
 	return fluid_player_get_status(_midi.player) == FLUID_PLAYER_PLAYING;
@@ -149,6 +169,9 @@ bool MusicDriver_FluidSynth::IsSongPlayi
 
 void MusicDriver_FluidSynth::SetVolume(byte vol)
 {
+	std::lock_guard<std::mutex> lock{ _midi.synth_mutex };
+	if (_midi.settings == nullptr) return;
+
 	/* Allowed range of synth.gain is 0.0 to 10.0 */
 	/* fluidsynth's default gain is 0.2, so use this as "full
 	 * volume". Set gain using OpenTTD's volume, as a number between 0