diff --git a/radio/src/os/async_freertos.cpp b/radio/src/os/async_freertos.cpp
index 61d99468a..4e88a6351 100644
--- a/radio/src/os/async_freertos.cpp
+++ b/radio/src/os/async_freertos.cpp
@@ -19,6 +19,7 @@
  * GNU General Public License for more details.
  */
 
+#include "task.h"
 #include "async.h"
 
 #include <FreeRTOS/include/FreeRTOS.h>
@@ -27,7 +28,7 @@
 bool async_call(async_func_t func, volatile bool* excl_flag, void* param1,
                 uint32_t param2)
 {
-  if (xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED) {
+  if (scheduler_is_running()) {
 
     // check exclusive flag first
     if (excl_flag && *excl_flag) return false;
@@ -48,7 +49,7 @@ bool async_call_isr(async_func_t func, volatile bool* excl_flag, void* param1,
                     uint32_t param2)
 {
   BaseType_t xHigherPriorityTaskWoken = pdFALSE;
-  if (xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED) {
+  if (scheduler_is_running()) {
 
     // check exclusive flag first
     if (excl_flag && *excl_flag) return false;
diff --git a/radio/src/os/task.h b/radio/src/os/task.h
index 491f17cd8..e1a62ed93 100644
--- a/radio/src/os/task.h
+++ b/radio/src/os/task.h
@@ -38,6 +38,8 @@ void task_create(task_handle_t* h, task_func_t func, const char* name,
 unsigned task_get_stack_usage(task_handle_t* h);
 unsigned task_get_stack_size(task_handle_t* h);
 
+bool scheduler_is_running();
+
 void mutex_create(mutex_handle_t* h);
 bool mutex_lock(mutex_handle_t* h);
 void mutex_unlock(mutex_handle_t* h);
@@ -49,6 +51,7 @@ bool mutex_trylock(mutex_handle_t* h);
  *
  * void doWork()
  * {
+ *
  *   MutexLock lock = MutexLock::MakeInstance(mutex);
  *   while(!queue.isEmpty)
  *   {
@@ -97,9 +100,9 @@ class MutexLock
 {
 public:
   static MutexLock MakeInstance(mutex_handle_t* mtx) {return MutexLock(mtx);}
-  ~MutexLock() {if(locked) mutex_unlock(mutex);}
-  void lock() {if(!locked) mutex_lock(mutex); locked=true;}
-  void unlock() {if(locked) mutex_unlock(mutex); locked=false;}
+  ~MutexLock() {if(!scheduler_is_running()) return; if(locked) mutex_unlock(mutex);}
+  void lock() {if(!scheduler_is_running()) return; if(!locked) mutex_lock(mutex); locked=true;}
+  void unlock() {if(!scheduler_is_running()) return; if(locked) mutex_unlock(mutex); locked=false;}
 
   MutexLock(const MutexLock&)               = delete;
   MutexLock(MutexLock&&)                    = delete;
@@ -110,7 +113,7 @@ public:
   static void  operator delete  (void*)     = delete;
   static void  operator delete[](void*)     = delete;
 private:
-  MutexLock(mutex_handle_t* mtx):mutex(mtx),locked(false) {mutex_lock(mutex); locked = true;}
+  MutexLock(mutex_handle_t* mtx):mutex(mtx),locked(false) {if(!scheduler_is_running()) return; mutex_lock(mutex); locked = true;}
   mutex_handle_t* mutex;
   bool locked;
 };
diff --git a/radio/src/os/task_freertos.cpp b/radio/src/os/task_freertos.cpp
index 3eedbb0ee..d6745e5c9 100644
--- a/radio/src/os/task_freertos.cpp
+++ b/radio/src/os/task_freertos.cpp
@@ -47,6 +47,13 @@ unsigned task_get_stack_size(task_handle_t* h)
   return h->_stack_size * sizeof(StackType_t);
 }
 
+bool scheduler_is_running()
+{
+  if (xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED)
+    return true;
+  return false;
+}
+
 void mutex_create(mutex_handle_t* h)
 {
   h->_rtos_handle = xSemaphoreCreateMutexStatic(&h->_mutex_struct);
diff --git a/radio/src/os/task_native.cpp b/radio/src/os/task_native.cpp
index 04a387b67..290c5914c 100644
--- a/radio/src/os/task_native.cpp
+++ b/radio/src/os/task_native.cpp
@@ -130,6 +130,11 @@ unsigned task_get_stack_size(task_handle_t* h)
   return h->_stack_size * 4;
 }
 
+bool scheduler_is_running()
+{
+  return true;
+}
+
 void mutex_create(mutex_handle_t* h)
 {
   (void)h;
diff --git a/radio/src/targets/common/arm/stm32/stm32_i2c_driver.cpp b/radio/src/targets/common/arm/stm32/stm32_i2c_driver.cpp
index eb8570231..ad4f0e16a 100644
--- a/radio/src/targets/common/arm/stm32/stm32_i2c_driver.cpp
+++ b/radio/src/targets/common/arm/stm32/stm32_i2c_driver.cpp
@@ -35,8 +35,9 @@
 struct stm32_i2c_device {
   I2C_HandleTypeDef handle;
   const stm32_i2c_hw_def_t* hw_def;
-#if !defined(BOOT) && !defined(RADIO_PA01)
+#if !defined(BOOT)
   mutex_handle_t mutex;
+  bool mutex_initialized;
 #endif
 };
 
@@ -54,8 +55,16 @@ static I2C_HandleTypeDef* i2c_get_handle(uint8_t bus)
   return &_i2c_devs[bus].handle;
 }
 
-#if !defined(BOOT) && !defined(RADIO_PA01)
-#define I2CMutex(bus) MutexLock mutexLock = MutexLock::MakeInstance(&i2c_get_device(bus)->mutex)
+#if !defined(BOOT)
+static void i2c_ensure_mutex(stm32_i2c_device* dev)
+{
+  if (!dev->mutex_initialized && scheduler_is_running()) {
+    mutex_create(&dev->mutex);
+    dev->mutex_initialized = true;
+  }
+}
+
+#define I2CMutex(bus) i2c_ensure_mutex(i2c_get_device(bus)); MutexLock mutexLock = MutexLock::MakeInstance(&i2c_get_device(bus)->mutex)
 #else
 #define I2CMutex(bus)
 #endif
@@ -525,8 +534,8 @@ int stm32_i2c_init(uint8_t bus, uint32_t clock_rate, const stm32_i2c_hw_def_t* h
   }
 #endif
 
-#if !defined(BOOT) && !defined(RADIO_PA01)
-  mutex_create(&dev->mutex);
+#if !defined(BOOT)
+  dev->mutex_initialized = false;
 #endif
   return 1;
 }