diff --git a/Firmware/mmu2_log.h b/Firmware/mmu2_log.h
index bc4313294..1d18a2b6d 100644
--- a/Firmware/mmu2_log.h
+++ b/Firmware/mmu2_log.h
@@ -1,7 +1,7 @@
 #pragma once
-
-#ifndef UNITTEST
-#include "Marlin.h"
+#ifdef __AVR__
+    #include <avr/pgmspace.h>
+#endif
 
 // Beware - before changing this prefix, think twice
 // you'd need to change appmain.cpp app_marlin_serial_output_write_hook
@@ -14,16 +14,22 @@ namespace MMU2 {
 /// @param msg pointer to a string in PROGMEM
 /// On the AVR platform this variant reads the input string from PROGMEM.
 /// On the ARM platform it calls LogErrorEvent directly (silently expecting the compiler to optimize it away)
-void LogErrorEvent_P(const char *msg);
+void LogErrorEvent_P(const char *msg_P);
 
 /// Report the msg into the general logging subsystem (through Marlin's SERIAL_ECHO stuff)
 /// @param msg pointer to a string in PROGMEM
 /// On the AVR platform this variant reads the input string from PROGMEM.
 /// On the ARM platform it calls LogErrorEvent directly (silently expecting the compiler to optimize it away)
-void LogEchoEvent_P(const char *msg);
+void LogEchoEvent_P(const char *msg_P);
 
-} // namespace
+} // namespace MMU2
 
+#ifndef UNITTEST
+    #ifdef __AVR__
+        #include "Marlin.h"
+    #else
+        #include "../../core/serial.h"
+    #endif
     #define SERIAL_MMU2() \
         { serialprintPGM(mmu2Magic); }
 
@@ -49,11 +55,14 @@ void LogEchoEvent_P(const char *msg);
         } while (0)
     #define MMU2_ERROR_MSG(S) MMU2_ECHO_MSG(S) //!@todo Decide MMU errors  on serial line
 
-#else // #ifndef UNITTEST
+#else                                          // #ifndef UNITTEST
+    #include "stubs/stub_interfaces.h"
+    #define MMU2_ECHO_MSGLN(S)    marlinLogSim.AppendLine(S)
+    #define MMU2_ERROR_MSGLN(S)   marlinLogSim.AppendLine(S)
+    #define MMU2_ECHO_MSGRPGM(S)  /*marlinLogSim.AppendLine(S)*/
+    #define MMU2_ERROR_MSGRPGM(S) /*marlinLogSim.AppendLine(S)*/
+    #define SERIAL_ECHOLNPGM(S)   /*marlinLogSim.AppendLine(S)*/
+    #define SERIAL_ECHOPGM(S)     /* */
+    #define SERIAL_ECHOLN(S)      /*marlinLogSim.AppendLine(S)*/
 
-    #define MMU2_ECHO_MSGLN(S)    /* */
-    #define MMU2_ERROR_MSGLN(S)   /* */
-    #define MMU2_ECHO_MSGRPGM(S)  /* */
-    #define MMU2_ERROR_MSGRPGM(S) /* */
-
-#endif // #ifndef UNITTEST
+#endif                            // #ifndef UNITTEST