diff --git a/Marlin/src/feature/mmu3/mmu3_protocol_logic.cpp b/Marlin/src/feature/mmu3/mmu3_protocol_logic.cpp
index cf74e669b8..4323925b6b 100644
--- a/Marlin/src/feature/mmu3/mmu3_protocol_logic.cpp
+++ b/Marlin/src/feature/mmu3/mmu3_protocol_logic.cpp
@@ -707,7 +707,7 @@ namespace MMU3 {
   }
 
   bool ProtocolLogic::Elapsed(uint32_t timeout) const {
-    return _millis() >= (lastUARTActivityMs + timeout);
+    return ELAPSED(_millis(), lastUARTActivityMs + timeout);
   }
 
   void ProtocolLogic::RecordUARTActivity() {
@@ -716,7 +716,7 @@ namespace MMU3 {
 
   void ProtocolLogic::RecordReceivedByte(uint8_t c) {
     lastReceivedBytes[lrb] = c;
-    lrb = (lrb + 1) % lastReceivedBytes.size();
+    lrb = (lrb + 1) % COUNT(lastReceivedBytes);
   }
 
   constexpr char NibbleToChar(uint8_t c) {
@@ -728,13 +728,13 @@ namespace MMU3 {
   }
 
   void ProtocolLogic::FormatLastReceivedBytes(char *dst) {
-    for (uint8_t i = 0; i < lastReceivedBytes.size(); ++i) {
-      uint8_t b = lastReceivedBytes[(lrb - i - 1) % lastReceivedBytes.size()];
+    for (uint8_t i = 0; i < COUNT(lastReceivedBytes); ++i) {
+      uint8_t b = lastReceivedBytes[(COUNT(lastReceivedBytes) - 1 + (lrb - i)) % COUNT(lastReceivedBytes)];
       dst[i * 3] = NibbleToChar(b >> 4);
       dst[i * 3 + 1] = NibbleToChar(b & 0xf);
       dst[i * 3 + 2] = ' ';
     }
-    dst[(lastReceivedBytes.size() - 1) * 3 + 2] = 0; // terminate properly
+    dst[(COUNT(lastReceivedBytes) - 1) * 3 + 2] = 0; // terminate properly
   }
 
   void ProtocolLogic::FormatLastResponseMsgAndClearLRB(char *dst) {
@@ -777,18 +777,18 @@ namespace MMU3 {
   }
 
   void ProtocolLogic::LogError(const char *reason_P) {
-    char lrb[lastReceivedBytes.size() * 3];
-    FormatLastReceivedBytes(lrb);
+    char _lrb[COUNT(lastReceivedBytes) * 3];
+    FormatLastReceivedBytes(_lrb);
 
     MMU2_ERROR_MSGRPGM(reason_P);
     SERIAL_ECHOPGM(", last bytes: ");
-    SERIAL_ECHOLN(lrb);
+    SERIAL_ECHOLN(_lrb);
   }
 
   void ProtocolLogic::LogResponse() {
-    char lrb[lastReceivedBytes.size()];
-    FormatLastResponseMsgAndClearLRB(lrb);
-    MMU2_ECHO_MSGLN(lrb);
+    char _lrb[COUNT(lastReceivedBytes)];
+    FormatLastResponseMsgAndClearLRB(_lrb);
+    MMU2_ECHO_MSGLN(_lrb);
   }
 
   StepStatus ProtocolLogic::SuppressShortDropOuts(const char *msg_P, StepStatus ss) {
diff --git a/Marlin/src/feature/mmu3/mmu3_protocol_logic.h b/Marlin/src/feature/mmu3/mmu3_protocol_logic.h
index 2fef77c276..30f9c5d0d5 100644
--- a/Marlin/src/feature/mmu3/mmu3_protocol_logic.h
+++ b/Marlin/src/feature/mmu3/mmu3_protocol_logic.h
@@ -36,24 +36,8 @@
   #include "mmu_hw/buttons.h"
   #include "mmu_hw/registers.h"
   #include "mmu3_protocol.h"
-
-  // #include <array> std array is not available on AVR ... we need to "fake" it
-  namespace std {
-    template <typename T, uint8_t N>
-    class array {
-      T data[N];
-      public:
-      array() = default;
-      inline constexpr T *begin() const { return data; }
-      inline constexpr T *end() const { return data + N; }
-      static constexpr uint8_t size() { return N; }
-      inline T &operator[](uint8_t i) { return data[i]; }
-    };
-  } // std
-
 #else // !__AVR__
 
-  #include <array>
   #include "mmu_hw/error_codes.h"
   #include "mmu_hw/progress_codes.h"
 
@@ -351,8 +335,7 @@ namespace MMU3 {
 
     Protocol protocol;                       //!< protocol codec
 
-    std::array<uint8_t, 16> lastReceivedBytes; //!< remembers the last few bytes of incoming communication for diagnostic purposes
-    uint8_t lrb;
+    uint8_t lrb, lastReceivedBytes[16];      //!< keep the last few bytes of incoming communication for diagnostic purposes
 
     ErrorCode errorCode;        //!< last received error code from the MMU
     ProgressCode progressCode;  //!< last received progress code from the MMU