diff --git a/templates/api/src/plugin_api.h b/templates/api/src/plugin_api.h
index a1ce7a5..327db47 100644
--- a/templates/api/src/plugin_api.h
+++ b/templates/api/src/plugin_api.h
@@ -28,6 +28,8 @@ typedef struct {
 	const char * (*get_datadir)(void *handle);
 	int (*write_state)(void *handle, const char *data, size_t length);
 	void (*load_parameter)(void *handle, size_t index, float value);
+	void (*lock_state)(void *handle);
+	void (*unlock_state)(void *handle);
 } plugin_callbacks;
 
 typedef struct {
diff --git a/templates/lv2/src/lv2.c b/templates/lv2/src/lv2.c
index 37ebe8c..1355e3e 100644
--- a/templates/lv2/src/lv2.c
+++ b/templates/lv2/src/lv2.c
@@ -57,6 +57,24 @@
 # include <pmmintrin.h>
 #endif
 
+#if (DATA_PRODUCT_CONTROL_INPUTS_N > 0) && defined(DATA_STATE_DSP_CUSTOM)
+# include <stdatomic.h>
+# if defined(_WIN32) || defined(__CYGWIN__)
+#  include <processthreadsapi.h>
+#  define yield SwitchToThread
+# else
+#  include <sched.h>
+#  define yield sched_yield
+# endif
+#endif
+
+#define CONTROL_INPUT_INDEX_OFFSET ( \
+		DATA_PRODUCT_AUDIO_INPUT_CHANNELS_N \
+		+ DATA_PRODUCT_AUDIO_OUTPUT_CHANNELS_N \
+		+ DATA_PRODUCT_MIDI_INPUTS_N \
+		+ DATA_PRODUCT_MIDI_OUTPUTS_N )
+#define CONTROL_OUTPUT_INDEX_OFFSET	(CONTROL_INPUT_INDEX_OFFSET + DATA_PRODUCT_CONTROL_INPUTS_N)
+
 #if DATA_PRODUCT_CONTROL_INPUTS_N > 0
 static inline float clampf(float x, float m, float M) {
 	return x < m ? m : (x > M ? M : x);
@@ -92,6 +110,12 @@ typedef struct {
 #endif
 #if DATA_PRODUCT_CONTROL_INPUTS_N > 0
 	float				params[DATA_PRODUCT_CONTROL_INPUTS_N];
+# ifdef DATA_STATE_DSP_CUSTOM
+	float				params_sync[DATA_PRODUCT_CONTROL_INPUTS_N];
+	atomic_flag			sync_lock_flag;
+	char				synced;
+	char				loaded;
+# endif
 #endif
 	void *				mem;
 	char *				bundle_path;
@@ -122,12 +146,24 @@ static int write_state_cb(void *handle, const char *data, size_t length) {
 # if DATA_PRODUCT_CONTROL_INPUTS_N > 0
 static void load_parameter_cb(void *handle, size_t index, float value) {
 	plugin_instance * i = (plugin_instance *)handle;
-	size_t idx = index_to_param[index];
+	size_t idx = index_to_param[index] - CONTROL_INPUT_INDEX_OFFSET;
 	value = adjust_param(idx, value);
-	i->params[idx] = value;
-	plugin_set_parameter(&i->p, index, value);
+	i->params_sync[idx] = value;
+	i->loaded = 1;
 }
 # endif
+
+static void lock_state_cb(void *handle) {
+	plugin_instance * i = (plugin_instance *)handle;
+	while (atomic_flag_test_and_set(&i->sync_lock_flag))
+		yield();
+	i->synced = 0;
+}
+
+static void unlock_state_cb(void *handle) {
+	plugin_instance * i = (plugin_instance *)handle;
+	atomic_flag_clear(&i->sync_lock_flag);
+}
 #endif
 
 static LV2_Handle instantiate(const struct LV2_Descriptor * descriptor, double sample_rate, const char * bundle_path, const LV2_Feature * const * features) {
@@ -175,13 +211,17 @@ static LV2_Handle instantiate(const struct LV2_Descriptor * descriptor, double s
 # ifdef DATA_STATE_DSP_CUSTOM
 		/* .write_state		= */ write_state_cb,
 #  if DATA_PRODUCT_CONTROL_INPUTS_N > 0
-		/* .load_parameter	= */ load_parameter_cb
+		/* .load_parameter	= */ load_parameter_cb,
 #  else
-		/* .load_parameter	= */ NULL
+		/* .load_parameter	= */ NULL,
 #  endif
+		/* .lock_state		= */ lock_state_cb,
+		/* .unlock_state	= */ unlock_state_cb
 # else
 		/* .write_state		= */ NULL,
-		/* .load_parameter	= */ NULL
+		/* .load_parameter	= */ NULL,
+		/* .state_lock		= */ NULL,
+		/* .state_unlock	= */ NULL
 # endif
 	};
 	plugin_init(&instance->p, &cbs);
@@ -275,6 +315,15 @@ static void activate(LV2_Handle instance) {
 		i->params[j] = i->c[j] != NULL ? *i->c[j] : param_data[j].def;
 		plugin_set_parameter(&i->p, param_data[j].index, i->params[j]);
 	}
+# ifdef DATA_STATE_DSP_CUSTOM
+	for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++)
+		i->params_sync[j] = i->params[j];
+	// why is this not correct?
+	// i->sync_lock_flag = ATOMIC_FLAG_INIT;
+	atomic_flag_clear(&i->sync_lock_flag);
+	i->synced = 1;
+	i->loaded = 0;
+# endif
 #endif
 	plugin_reset(&i->p);
 }
@@ -295,15 +344,47 @@ static void run(LV2_Handle instance, uint32_t sample_count) {
 #endif
 
 #if DATA_PRODUCT_CONTROL_INPUTS_N > 0
-	for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++) {
-		if (i->c[j] == NULL)
-			continue;
-		float v = adjust_param(j, *i->c[j]);
-		if (v != i->params[j]) {
-			i->params[j] = v;
-			plugin_set_parameter(&i->p, param_data[j].index, v);
+# ifdef DATA_STATE_DSP_CUSTOM
+	if (!atomic_flag_test_and_set(&i->sync_lock_flag)) {
+		if (!i->synced) {
+			if (i->loaded) {
+				for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++) {
+					i->params[j] = i->params_sync[j];
+					plugin_set_parameter(&i->p, param_data[j].index, i->params[j]);
+				}
+			} else {
+				for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++)
+					if (i->params[j] != i->params_sync[j]) {
+						i->params_sync[j] = i->params[j];
+						plugin_set_parameter(&i->p, param_data[j].index, i->params[j]);
+					}
+			}
+		}
+		i->synced = 1;
+		i->loaded = 0;
+		atomic_flag_clear(&i->sync_lock_flag);
+# endif
+
+		for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++) {
+			if (i->c[j] == NULL)
+				continue;
+			float v = adjust_param(j, *i->c[j]);
+			if (v != i->params[j]) {
+				i->params[j] = v;
+				plugin_set_parameter(&i->p, param_data[j].index, v);
+			}
+		}
+# ifdef DATA_STATE_DSP_CUSTOM
+	} else {
+		for (uint32_t j = 0; j < DATA_PRODUCT_CONTROL_INPUTS_N; j++) {
+			if (i->c[j] == NULL)
+				continue;
+			float v = adjust_param(j, *i->c[j]);
+			if (v != i->params[j])
+				i->params[j] = v;
 		}
 	}
+# endif
 #endif
 
 #if DATA_PRODUCT_MIDI_INPUTS_N > 0
@@ -429,13 +510,6 @@ typedef struct {
 # endif
 } ui_instance;
 
-# define CONTROL_INPUT_INDEX_OFFSET ( \
-		DATA_PRODUCT_AUDIO_INPUT_CHANNELS_N \
-		+ DATA_PRODUCT_AUDIO_OUTPUT_CHANNELS_N \
-		+ DATA_PRODUCT_MIDI_INPUTS_N \
-		+ DATA_PRODUCT_MIDI_OUTPUTS_N )
-# define CONTROL_OUTPUT_INDEX_OFFSET	(CONTROL_INPUT_INDEX_OFFSET + DATA_PRODUCT_CONTROL_INPUTS_N)
-
 static const char * ui_get_bundle_path_cb(void *handle) {
 	ui_instance *instance = (ui_instance *)handle;
 	return instance->bundle_path;
diff --git a/test/plugin.h b/test/plugin.h
index d64da73..45b6bde 100644
--- a/test/plugin.h
+++ b/test/plugin.h
@@ -141,18 +141,30 @@ static float parse_float(const uint8_t *data) {
 
 static int plugin_state_save(plugin *instance) {
 	uint8_t data[13];
-	serialize_float(data, instance->gain);
-	serialize_float(data + 4, instance->delay);
-	serialize_float(data + 8, instance->cutoff);
-	data[12] = instance->bypass ? 1 : 0;
+	instance->cbs.lock_state(instance->cbs.handle);
+	const float gain = instance->gain;
+	const float delay = instance->delay;
+	const float cutoff = instance->cutoff;
+	const char bypass = instance->bypass;
+	instance->cbs.unlock_state(instance->cbs.handle);
+	serialize_float(data, gain);
+	serialize_float(data + 4, delay);
+	serialize_float(data + 8, cutoff);
+	data[12] = bypass ? 1 : 0;
 	return instance->cbs.write_state(instance->cbs.handle, (const char *)data, 13);
 }
 
 static void plugin_state_load(plugin *instance, const char *data, size_t length) {
 	(void)length;
 	const uint8_t *d = (const uint8_t *)data;
-	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_gain, parse_float(d));
-	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_delay, parse_float(d + 4));
-	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_cutoff, parse_float(d + 8));
-	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_bypass, d[12] ? 1.f : 0.f);
+	const float gain = parse_float(d);
+	const float delay = parse_float(d + 4);
+	const float cutoff = parse_float(d + 8);
+	const float bypass = d[12] ? 1.f : 0.f;
+	instance->cbs.lock_state(instance->cbs.handle);
+	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_gain, gain);
+	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_delay, delay);
+	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_cutoff, cutoff);
+	instance->cbs.load_parameter(instance->cbs.handle, plugin_parameter_bypass, bypass);
+	instance->cbs.unlock_state(instance->cbs.handle);
 }