diff --git a/src/asynStreamGeneratorDriver.cpp b/src/asynStreamGeneratorDriver.cpp
index 4d816b0..3e1ae89 100644
--- a/src/asynStreamGeneratorDriver.cpp
+++ b/src/asynStreamGeneratorDriver.cpp
@@ -444,13 +444,13 @@ asynStatus asynStreamGeneratorDriver::writeInt32(asynUser *pasynUser,
     } else if (function == P_EnableElectronics) {
         if (value) {
             setIntegerParam(function, 1);
-            CommandHeader ch(start);
+            CommandHeader ch(CommandId::start);
             std::size_t written;
             pasynOctetSyncIO->write(pasynUDPUser, (char *)&ch, sizeof(ch), 1,
                                     &written);
         } else {
             setIntegerParam(function, 0);
-            CommandHeader ch(stop);
+            CommandHeader ch(CommandId::stop);
             std::size_t written;
             pasynOctetSyncIO->write(pasynUDPUser, (char *)&ch, sizeof(ch), 1,
                                     &written);
@@ -566,6 +566,8 @@ void asynStreamGeneratorDriver::normaliseUDP() {
 
             lastBufferNumber[header->McpdID] = header->BufferNumber;
 
+            // TODO I think monitor and detector events aren't mixed, so we
+            // could do the check once
             for (std::size_t i = 0; i < total_events; ++i) {
                 char *event = (buffer + 21 * 2 + i * 6);
                 const bool isMonitorEvent = event[5] & 0x80;
diff --git a/src/asynStreamGeneratorDriver.h b/src/asynStreamGeneratorDriver.h
index f5c1db1..bd7be9d 100644
--- a/src/asynStreamGeneratorDriver.h
+++ b/src/asynStreamGeneratorDriver.h
@@ -12,7 +12,12 @@
 /*******************************************************************************
  * UDP Packet Definitions
  */
-enum CommandId : std::int16_t { reset = 0, start = 1, stop = 2, cont = 3 };
+enum class CommandId : std::uint16_t {
+    reset = 0,
+    start = 1,
+    stop = 2,
+    cont = 3
+};
 
 struct __attribute__((__packed__)) CommandHeader {
     uint16_t BufferLength;
@@ -29,8 +34,11 @@ struct __attribute__((__packed__)) CommandHeader {
 
     CommandHeader(const CommandId commandId)
         : BufferLength(10), BufferType(0x8000), HeaderLength(10),
-          BufferNumber(0), Command(commandId), McpdIdStatus(0), TimeStampLo(0),
-          TimeStampMid(0), TimeStampHigh(0), Checksum(0), Finalizer(0xffff) {
+          BufferNumber(0),
+          Command(
+              static_cast<std::underlying_type<CommandId>::type>(commandId)),
+          McpdIdStatus(0), TimeStampLo(0), TimeStampMid(0), TimeStampHigh(0),
+          Checksum(0), Finalizer(0xffff) {
 
         Checksum = BufferLength ^ BufferType ^ HeaderLength ^ BufferNumber ^
                    Command ^ McpdIdStatus ^ TimeStampLo ^ TimeStampMid ^
@@ -66,11 +74,12 @@ struct __attribute__((__packed__)) DetectorEvent {
     uint16_t Amplitude : 8;
     uint16_t Id : 1;
     inline uint32_t nanosecs() const { return TimeStamp * 100; }
-    inline uint64_t pixelId(uint32_t mpcdId) const {
+    inline uint32_t pixelId(uint32_t mpcdId) const {
         const uint32_t x_pixels = 128;
         const uint32_t y_pixels = 128;
         return (mpcdId - 1) * x_pixels * y_pixels +
-               x_pixels * (uint32_t)this->XPosition + (uint32_t)this->YPosition;
+               x_pixels * (uint32_t)(this->XPosition >> 3) +
+               (uint32_t)(this->YPosition >> 3);
     }
 };