diff --git a/Makefile-ARM b/Makefile-ARM
index 4bb7fed..a288a25 100644
--- a/Makefile-ARM
+++ b/Makefile-ARM
@@ -119,6 +119,7 @@ CFLAGS += -Os
 CFLAGS += -flto
 CFLAGS += -ffunction-sections
 CFLAGS += -fdata-sections
+#CFLAGS += -dM -E # To list all predefined macros into the .o file.
 # Until we're done with basic porting ...
 CFLAGS += -D__ARMEL_NOTYET__
 
diff --git a/Makefile-AVR b/Makefile-AVR
index 728dd98..28e61ec 100644
--- a/Makefile-AVR
+++ b/Makefile-AVR
@@ -133,6 +133,7 @@ CFLAGS += -ffunction-sections
 CFLAGS += -finline-functions-called-once
 CFLAGS += -mcall-prologues
 CFLAGS += -Wa,-adhlns=$(@:.o=.al)
+#CFLAGS += -dM -E # To list all predefined macros into the .o file.
 
 LDFLAGS  = -Wl,--as-needed
 
diff --git a/Makefile-SIM b/Makefile-SIM
index 60fff20..dfc2e01 100644
--- a/Makefile-SIM
+++ b/Makefile-SIM
@@ -48,6 +48,7 @@ CFLAGS  = $(EXTRA_CFLAGS)
 CFLAGS += -g -Wall -Wstrict-prototypes -Wno-format -Os $(DEFS) -std=gnu99
 CFLAGS += -funsigned-char -funsigned-bitfields -fshort-enums -I.. -I.
 CFLAGS += -DSIMULATOR -Wno-format -Wno-format-security
+#CFLAGS += -dM -E # To list all predefined macros into the .o file.
 
 # Satisfy all current config chip targets
 CFLAGS += -D__AVR_ATmega644__ -D__AVR_ATmega644A__ -D__AVR_ATmega644P__