diff --git a/doc/Extended-BASIC.md b/doc/Extended-BASIC.md
index eeccfae3..09e7dd35 100644
--- a/doc/Extended-BASIC.md
+++ b/doc/Extended-BASIC.md
@@ -67,13 +67,9 @@ Saves the binary data from the given memory area. NOTE: for now syntax differs f
 
 Resets the machine. In direct mode asks for confirmation first.
 
-### `FAST` (all)
+### `FAST`, `SLOW` (all)
 
-Tries to switch the machine to turbo mode - details differ depending on the configured machine / motherboard.
-
-### `SLOW` (all)
-
-Tries to switch the machine back to 1 MHz operation mode.
+Tries to switch the machine to turbo mode (or back to 1MHz operation mode) - details differ depending on the configured machine / motherboard. On MEGA65 motherboard this is not available in native mode, it is not designed to run in 1MHz due to using compound CPU instructions.
 
 ### `OLD` (all)
 
diff --git a/src/basic/,imports.s b/src/basic/,imports.s
index 62a37c08..225c956f 100644
--- a/src/basic/,imports.s
+++ b/src/basic/,imports.s
@@ -29,11 +29,13 @@
 
 ;; #ALIAS# SELDEV              = KERNAL_0.SELDEV
 
+;
+; MEGA65 specific parts
+;
+
 ;; #ALIAS# map_end             = KERNAL_0.map_end
 ;; #ALIAS# map_NORMAL          = KERNAL_0.map_NORMAL
 
 ;; #ALIAS# M65_MODEGET         = KERNAL_0.M65_MODEGET
 ;; #ALIAS# M65_MODESET         = KERNAL_0.M65_MODESET
-;; #ALIAS# M65_SLOW            = KERNAL_0.M65_SLOW
-;; #ALIAS# M65_FAST            = KERNAL_0.M65_FAST
 ;; #ALIAS# M65_SETWIN_Y        = KERNAL_0.M65_SETWIN_Y
diff --git a/src/basic/basic_commands_01/cmd__jumptable_01.s b/src/basic/basic_commands_01/cmd__jumptable_01.s
index 12152493..31ebb526 100644
--- a/src/basic/basic_commands_01/cmd__jumptable_01.s
+++ b/src/basic/basic_commands_01/cmd__jumptable_01.s
@@ -6,18 +6,9 @@
 ; Jumptable for BASIC commands with tokens prefixed by $01
 ;
 
-!ifdef CONFIG_MB_M65 {
-
-!set ITEM_00 = M65_SLOW
-!set ITEM_01 = M65_FAST
-
-} else {
 
 !set ITEM_00 = cmd_slow
 !set ITEM_01 = cmd_fast
-
-}
-
 !set ITEM_02 = cmd_old
 
 	; NOTE! These commands are temporarily placed here, they should be a part of list 02!
diff --git a/src/basic/basic_commands_01/cmd_fast_slow.s b/src/basic/basic_commands_01/cmd_fast_slow.s
index 7b7adb86..891494fe 100644
--- a/src/basic/basic_commands_01/cmd_fast_slow.s
+++ b/src/basic/basic_commands_01/cmd_fast_slow.s
@@ -5,6 +5,32 @@
 
 !ifdef CONFIG_MB_M65 {
 
+; NOTE: In native mode the system should not run at 1 MHz speed - it's dangerous,
+;       as it uses compound instructions, which are not safe in 1MHz mode
+
+cmd_slow: ; set CPU speed to 1 MHz
+
+	jsr helper_ensure_legacy_mode
+
+	lda #$40
+	bra cmd_slow_fast_common
+
+	; FALLTROUGH
+
+cmd_fast: ; set CPU speed to 40 MHz
+
+	jsr helper_ensure_legacy_mode
+
+	lda #$41
+
+	; FALLTROUGH
+
+cmd_slow_fast_common:
+
+	sta CPU_D6510
+	rts
+
+
 	; For MEGA65 Kernal routines are called directly
 
 } else ifdef CONFIG_MB_U64 {
diff --git a/src/basic/basic_commands_01/helper_ensure_legacy_mode_m65.s b/src/basic/basic_commands_01/helper_ensure_legacy_mode_m65.s
new file mode 100644
index 00000000..c49b21d2
--- /dev/null
+++ b/src/basic/basic_commands_01/helper_ensure_legacy_mode_m65.s
@@ -0,0 +1,10 @@
+;; #LAYOUT# M65 BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+
+helper_ensure_legacy_mode:
+
+	jsr M65_MODEGET
+	+bcc do_LEGACY_MODE_ONLY_error
+
+	rts
diff --git a/src/basic/engine_runtime/do_error.s b/src/basic/engine_runtime/do_error.s
index baf57e47..acfafcea 100644
--- a/src/basic/engine_runtime/do_error.s
+++ b/src/basic/engine_runtime/do_error.s
@@ -52,6 +52,14 @@ do_kernal_error:                       ; .A = KERNAL error code, also almost mat
 
 	; Error messages specific to Open ROMs BASIC dialect
 
+!ifdef CONFIG_MB_M65 {
+
+do_LEGACY_MODE_ONLY_error:
+	!byte $E6
+do_NATIVE_MODE_ONLY_error:
+	!byte $E6
+}
+
 do_MEMORY_CORRUPT_error:
 	!byte $E6
 
diff --git a/src/kernal/board_m65/mega65_imports.s b/src/kernal/board_m65/mega65_imports.s
index 8f5a6e78..b74001ec 100644
--- a/src/kernal/board_m65/mega65_imports.s
+++ b/src/kernal/board_m65/mega65_imports.s
@@ -9,8 +9,6 @@
 
 ;; #ALIAS# CHROUT                          = KERNAL_0.proxy_K1_CHROUT
 ;; #ALIAS# STOP                            = KERNAL_0.STOP
-;; #ALIAS# M65_SLOW                        = KERNAL_0.M65_SLOW
-;; #ALIAS# M65_FAST                        = KERNAL_0.M65_FAST
 ;; #ALIAS# M65_MODEGET                     = KERNAL_0.M65_MODEGET
 ;; #ALIAS# M65_SETWIN_XY                   = KERNAL_0.M65_SETWIN_XY
 ;; #ALIAS# M65_SETWIN_WH                   = KERNAL_0.M65_SETWIN_WH
diff --git a/src/kernal/extapi_m65/mega65__jumptable.s b/src/kernal/extapi_m65/mega65__jumptable.s
index c20b1b4f..301226a2 100644
--- a/src/kernal/extapi_m65/mega65__jumptable.s
+++ b/src/kernal/extapi_m65/mega65__jumptable.s
@@ -14,12 +14,6 @@ M65_JMODEGET:
 M65_JISMODESET:
 	jsr M65_MODESET
 
-M65_JSLOW:
-	jsr M65_SLOW
-
-M65_JFAST:
-	jsr M65_FAST
-
 M65_JSELDEV:
 	jsr SELDEV
 
diff --git a/src/kernal/extapi_m65/mega65_modeset.s b/src/kernal/extapi_m65/mega65_modeset.s
index 153a58a8..52a04236 100644
--- a/src/kernal/extapi_m65/mega65_modeset.s
+++ b/src/kernal/extapi_m65/mega65_modeset.s
@@ -25,13 +25,15 @@ m65_mode64:
 	jsr viciv_shutdown
 	jsr vicii_init
 
-	; Reenable interrupts
+	; Switch CPU speed back to normal
+
+	lda #$40
+	sta CPU_D6510
+
+	; Reenable interrupts and quit
 
 	cli
-
-	; Switch CPU speed back to slow and quit
-
-	jmp M65_SLOW
+	rts
 
 
 m65_mode65:
@@ -42,7 +44,8 @@ m65_mode65:
 
 	; Switch CPU speed to fast
 
-	jsr M65_FAST
+	lda #$41
+	sta CPU_D6510
 
 	; Set the magic string to mark native mode
 
diff --git a/src/kernal/extapi_m65/mega65_slow_fast.s b/src/kernal/extapi_m65/mega65_slow_fast.s
deleted file mode 100644
index 8e91796c..00000000
--- a/src/kernal/extapi_m65/mega65_slow_fast.s
+++ /dev/null
@@ -1,16 +0,0 @@
-;; #LAYOUT# M65 KERNAL_0 #TAKE
-;; #LAYOUT# *   *        #IGNORE
-
-
-M65_SLOW: ; set CPU speed to 1 MHz
-
-	lda #$40
-	+skip_2_bytes_trash_nvz
-
-	; FALLTROUGH
-
-M65_FAST: ; set CPU speed to 40 MHz
-
-	lda #$41
-	sta CPU_D6510
-	rts
diff --git a/tools/generate_strings.cc b/tools/generate_strings.cc
index 43d95f34..65690641 100644
--- a/tools/generate_strings.cc
+++ b/tools/generate_strings.cc
@@ -276,7 +276,9 @@ const StringEntryList GLOBAL_Errors =  { ListType::STRINGS_BASIC, "errors",
     { true,  true,  true,  true,  "EV7_28", "NOT IMPLEMENTED"          }, // this message actually differs from the CBM one
     { false, false, false, false, "EV7_29", "FILE READ"                }, // not used for now
     // STD    M65    U64    X16   --- error strings specific to Open ROMs, not present in CBM BASIC dialects
-    { true,  true,  true,  true,  "EOR_2A", "MEMORY CORRUPT"           },   
+    { true,  true,  true,  true,  "EOR_2A", "MEMORY CORRUPT"           },
+    { false, true,  false, false, "EOR_2B", "NATIVE MODE ONLY"         },   
+    { false, true,  false, false, "EOR_2C", "LEGACY MODE ONLY"         },   
 } };
 
 // BASIC errors - miscelaneous strings