diff --git a/clients/CMakeLists.txt b/clients/CMakeLists.txt
index a48af11a..367acc04 100644
--- a/clients/CMakeLists.txt
+++ b/clients/CMakeLists.txt
@@ -1,6 +1,6 @@
 if(SFIZZ_JACK)
     add_executable(sfizz_jack MidiHelpers.h jack_client.cpp)
-    target_link_libraries(sfizz_jack PRIVATE sfizz::sfizz sfizz::jack absl::flags_parse)
+    target_link_libraries(sfizz_jack PRIVATE sfizz::sfizz sfizz::jack sfizz::spin_mutex absl::flags_parse)
     sfizz_enable_lto_if_needed(sfizz_jack)
     install(TARGETS sfizz_jack DESTINATION ${CMAKE_INSTALL_BINDIR}
         COMPONENT "jack" OPTIONAL)
diff --git a/clients/jack_client.cpp b/clients/jack_client.cpp
index b9e5f5dd..46fff6b2 100644
--- a/clients/jack_client.cpp
+++ b/clients/jack_client.cpp
@@ -26,6 +26,7 @@
 #include <absl/flags/parse.h>
 #include <absl/flags/flag.h>
 #include <absl/types/span.h>
+#include <SpinMutex.h>
 #include <atomic>
 #include <cstddef>
 #include <ios>
@@ -38,11 +39,14 @@
 #include <string_view>
 #include <chrono>
 #include <thread>
+#include <mutex>
+#include <algorithm>
 
 static jack_port_t* midiInputPort;
 static jack_port_t* outputPort1;
 static jack_port_t* outputPort2;
 static jack_client_t* client;
+static SpinMutex processMutex;
 
 int process(jack_nframes_t numFrames, void* arg)
 {
@@ -51,6 +55,16 @@ int process(jack_nframes_t numFrames, void* arg)
     auto* buffer = jack_port_get_buffer(midiInputPort, numFrames);
     assert(buffer);
 
+    auto* leftOutput = reinterpret_cast<float*>(jack_port_get_buffer(outputPort1, numFrames));
+    auto* rightOutput = reinterpret_cast<float*>(jack_port_get_buffer(outputPort2, numFrames));
+
+    std::unique_lock<SpinMutex> lock { processMutex, std::try_to_lock };
+    if (!lock.owns_lock()) {
+        std::fill_n(leftOutput, numFrames, 0.0f);
+        std::fill_n(rightOutput, numFrames, 0.0f);
+        return 0;
+    }
+
     auto numMidiEvents = jack_midi_get_event_count(buffer);
     jack_midi_event_t event;
 
@@ -96,9 +110,6 @@ int process(jack_nframes_t numFrames, void* arg)
         }
     }
 
-    auto* leftOutput = reinterpret_cast<float*>(jack_port_get_buffer(outputPort1, numFrames));
-    auto* rightOutput = reinterpret_cast<float*>(jack_port_get_buffer(outputPort2, numFrames));
-
     float* stereoOutput[] = { leftOutput, rightOutput };
     synth->renderBlock(stereoOutput, numFrames);
 
@@ -112,6 +123,7 @@ int sampleBlockChanged(jack_nframes_t nframes, void* arg)
 
     auto* synth = reinterpret_cast<sfz::Sfizz*>(arg);
     // DBG("Sample per block changed to " << nframes);
+    std::lock_guard<SpinMutex> lock { processMutex };
     synth->setSamplesPerBlock(nframes);
     return 0;
 }
@@ -123,6 +135,7 @@ int sampleRateChanged(jack_nframes_t nframes, void* arg)
 
     auto* synth = reinterpret_cast<sfz::Sfizz*>(arg);
     // DBG("Sample rate changed to " << nframes);
+    std::lock_guard<SpinMutex> lock { processMutex };
     synth->setSampleRate(nframes);
     return 0;
 }