diff --git a/raptor_eagle_ccd.cpp b/raptor_eagle_ccd.cpp
index d22cc4a..e712993 100644
--- a/raptor_eagle_ccd.cpp
+++ b/raptor_eagle_ccd.cpp
@@ -1009,10 +1009,12 @@ void RaptorEagleCCD::startAquisition()
         throw std::system_error(RaptorEagleCCDError::ERROR_EXT_TRIGGER_MODE);
     }
 
-    std::lock_guard lock_guard(_acqProcessesMutex);
 
     if (_acqRingFreeBufferPtrs.empty()) {
         logDebug("There is no free image buffers! Try to shrink ring buffer ...");
+
+        std::lock_guard lock_guard(_acqProcessesMutex);
+
         if (_acqRingBuffer.size() < DEFAULT_ACQ_RING_BUFFER_MAX_SIZE) {  // shrink
             size_t N = 0;
             for (auto i = _acqRingBuffer.size(); i < DEFAULT_ACQ_RING_BUFFER_MAX_SIZE; ++i, ++N) {
@@ -1117,7 +1119,7 @@ void RaptorEagleCCD::startAquisition()
         std::this_thread::sleep_for(std::chrono::milliseconds(10));
         if ((std::chrono::utc_clock::now() - start) > CAMERA_START_ACQ_TIMEOUT) {
             logError("CANNOT START ACQUIRING!!!");
-            throw RaptorEagleCCDError::ERROR_CANNOT_START_ACQUISITION;
+            throw std::system_error(RaptorEagleCCDError::ERROR_CANNOT_START_ACQUISITION);
         }
     }
     acq_pars->startTime = setTriggerRegisterBit(CL_TRIGGER_MODE_SNAPSHOT_BIT);