diff --git a/c64/,,config_custom.s b/c64/,,config_custom.s
index 4465b483..a6ab5010 100644
--- a/c64/,,config_custom.s
+++ b/c64/,,config_custom.s
@@ -40,6 +40,8 @@
 // Memory model
 
 #define CONFIG_MEMORY_MODEL_38K
+// #define CONFIG_MEMORY_MODEL_46K               // please keep disabled for now
+// #define CONFIG_MEMORY_MODEL_50K               // please keep disabled for now
 // #define CONFIG_MEMORY_MODEL_60K
 
 
diff --git a/c64/aliases/,aliases_config.s b/c64/aliases/,aliases_config.s
index 3e14bbaa..42c8166b 100644
--- a/c64/aliases/,aliases_config.s
+++ b/c64/aliases/,aliases_config.s
@@ -121,6 +121,12 @@
 #if CONFIG_MEMORY_MODEL_38K
 	.eval selected++
 #endif
+#if CONFIG_MEMORY_MODEL_46K
+	.eval selected++
+#endif
+#if CONFIG_MEMORY_MODEL_50K
+	.eval selected++
+#endif
 #if CONFIG_MEMORY_MODEL_60K
 	.eval selected++
 #endif
diff --git a/c64/kernal/iec/iec_send_file_name.s b/c64/kernal/iec/iec_send_file_name.s
index b250612a..8d61cb20 100644
--- a/c64/kernal/iec/iec_send_file_name.s
+++ b/c64/kernal/iec/iec_send_file_name.s
@@ -20,6 +20,8 @@ iec_send_file_name_loop:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<FNADDR+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_FNADDR
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (FNADDR),y
 #endif
diff --git a/c64/kernal/iec/save_iec.s b/c64/kernal/iec/save_iec.s
index 324653c6..80e3f8c0 100644
--- a/c64/kernal/iec/save_iec.s
+++ b/c64/kernal/iec/save_iec.s
@@ -82,6 +82,8 @@ iec_save_loop:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<MEMUSS+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_MEMUSS
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (MEMUSS),y
 #endif
diff --git a/c64/kernal/iostack/load_save_common.s b/c64/kernal/iostack/load_save_common.s
index 000e88f8..7e1b7503 100644
--- a/c64/kernal/iostack/load_save_common.s
+++ b/c64/kernal/iostack/load_save_common.s
@@ -66,7 +66,12 @@ lvs_handle_byte_verify:
 	// Compare with stored byte
 	cmp TBTCNT
 
-#else
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+	ldy #0
+	jsr peek_under_roms_EAL
+
+#else // CONFIG_MEMORY_MODEL_38K
 
 	ldy #0
 	cmp (EAL),y
@@ -134,6 +139,8 @@ lvs_display_searching_for:
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<FNADDR+0
 	jsr peek_under_roms
+#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr peek_under_roms_FNADDR
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (FNADDR),y
 #endif
diff --git a/c64/kernal/memory/under_rom_routines.s b/c64/kernal/memory/under_rom_routines.s
index 25de7830..c43d908a 100644
--- a/c64/kernal/memory/under_rom_routines.s
+++ b/c64/kernal/memory/under_rom_routines.s
@@ -2,14 +2,94 @@
 // #LAYOUT# *   KERNAL_0 #TAKE
 // #LAYOUT# *   *        #IGNORE
 
+
+#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
+
+
+peek_under_roms_MEMUSS:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (MEMUSS), y
+
+	// FALLTROUGH
+
+peek_under_roms_finalize:
+
+	// Store value in a safe place
+
+	tax
+
+	// Restore memory mapping
+
+	pla
+	sta CPU_R6510
+
+	// Retrieve value and quit
+
+	txa
+	rts
+
+
+peek_under_roms_FNADDR:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (FNADDR), y
+
+	// Continue using common code
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+
+peek_under_roms_EAL:
+
+	// Store current memory mapping, unmap BASIC ROM
+
+	lda CPU_R6510
+	pha
+	and #$FE
+	sta CPU_R6510 
+
+	// Retrieve value from under ROMs
+
+	lda (EAL), y
+
+	// Continue using common code
+
+#if HAS_OPCODES_65C02
+	bra peek_under_roms_finalize
+#else
+	jmp peek_under_roms_finalize
+#endif
+
+
+#elif CONFIG_MEMORY_MODEL_60K
+
+
 // IMPORTANT:
 // These routines lengths cannot be changed without changing
-// the aliases for peek_under_roms, poke_under_roms etc
-// in ,aliases.s.
+// the aliases for peek_under_roms, poke_under_roms, etc.
 // Thus those addresses are expressed using formulae.
 
-#if CONFIG_MEMORY_MODEL_60K
-
 install_ram_routines:
 	// Copy routines into place
 	ldx #__ram_routines_end-__ram_routines_start-1
@@ -69,4 +149,5 @@ memmap_allram_routine:
 
 __ram_routines_end:
 
-#endif // CONFIG_MEMORY_MODEL_60K
+
+#endif
diff --git a/c64/kernal/rs232/close_rs232.s b/c64/kernal/rs232/close_rs232.s
index 7a254c8d..d2f73820 100644
--- a/c64/kernal/rs232/close_rs232.s
+++ b/c64/kernal/rs232/close_rs232.s
@@ -14,6 +14,10 @@
 	.error "CONFIG_MEMORY_MODEL_60K is not compatible with RS-232 memory allocation code"
 #endif
 
+#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
+	.error "TODO: add compatibility with these memory models"
+#endif
+
 
 close_rs232:
 
diff --git a/c64/kernal/rs232/open_rs232.s b/c64/kernal/rs232/open_rs232.s
index 06c08e65..fc9a1c7c 100644
--- a/c64/kernal/rs232/open_rs232.s
+++ b/c64/kernal/rs232/open_rs232.s
@@ -14,6 +14,9 @@
 	.error "CONFIG_MEMORY_MODEL_60K is not compatible with RS-232 memory allocation code"
 #endif
 
+#if CONFIG_MEMORY_MODEL_46K ||CONFIG_MEMORY_MODEL_50K
+	.error "TODO: add compatibility with these memory models"
+#endif
 
 open_rs232: