diff --git a/Makefile b/Makefile
index 2487475..9ce1c39 100644
--- a/Makefile
+++ b/Makefile
@@ -46,44 +46,44 @@ SRCS_BASE_F256       = cartridge.c \
                        C256/jumptable.s
 
 ifeq ($(UNIT),F256)
-	TOOLCHAIN            = 65816
-	SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256jr.c
-	CFLAGS_FOR_UNIT      = -DMODEL=2 -DCPU=255 --target=f256
-	LDFLAGS_FOR_UNIT_ROM = src/C256/f256-flash.scm --cstartup=f256
-	LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
+    TOOLCHAIN            = 65816
+    SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256jr.c
+    CFLAGS_FOR_UNIT      = -DMODEL=2 -DCPU=255 --target=f256
+    LDFLAGS_FOR_UNIT_ROM = src/C256/f256-flash.scm --cstartup=f256
+    LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
 else ifeq ($(UNIT),F256JR2)
-	TOOLCHAIN            = 65816
-	SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256jr.c
-	CFLAGS_FOR_UNIT      = -DMODEL=35 -DCPU=255 --target=f256
-	LDFLAGS_FOR_UNIT_ROM = src/C256/f256k2-flash.scm --cstartup=f256
-	LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
+    TOOLCHAIN            = 65816
+    SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256jr.c
+    CFLAGS_FOR_UNIT      = -DMODEL=35 -DCPU=255 --target=f256
+    LDFLAGS_FOR_UNIT_ROM = src/C256/f256k2-flash.scm --cstartup=f256
+    LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
 else ifeq ($(UNIT),F256K)
-	TOOLCHAIN            = 65816
-	SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256k.c
-	CFLAGS_FOR_UNIT      = -DMODEL=18 -DCPU=255 --target=f256
-	LDFLAGS_FOR_UNIT_ROM = src/C256/f256-flash.scm --cstartup=f256
-	LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
+    TOOLCHAIN            = 65816
+    SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256k.c
+    CFLAGS_FOR_UNIT      = -DMODEL=18 -DCPU=255 --target=f256
+    LDFLAGS_FOR_UNIT_ROM = src/C256/f256-flash.scm --cstartup=f256
+    LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
 else ifeq ($(UNIT),F256K2)
-	TOOLCHAIN            = 65816
-	SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256k.c
-	CFLAGS_FOR_UNIT      = -DMODEL=17 -DCPU=255 --target=f256
-	LDFLAGS_FOR_UNIT_ROM = src/C256/f256k2-flash.scm --cstartup=f256
-	LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
+    TOOLCHAIN            = 65816
+    SRCS_FOR_UNIT        = $(SRCS_BASE_F256) dev/kbd_f256k.c
+    CFLAGS_FOR_UNIT      = -DMODEL=17 -DCPU=255 --target=f256
+    LDFLAGS_FOR_UNIT_ROM = src/C256/f256k2-flash.scm --cstartup=f256
+    LDFLAGS_FOR_UNIT_RAM = src/C256/f256-ld_lc.scm --cstartup=f256
 else
-	$(error "Unrecognized UNIT: $(UNIT)")
+    $(error Unrecognized UNIT: "$(UNIT)")
 endif
 
 ifeq ($(TOOLCHAIN),65816)
-	ifeq ($(strip $(CALYPSI_65816_ROOT)),)
-		$(error "Please set CALYPSI_65816_ROOT in your environment!")
-	endif
+    ifeq ($(strip $(CALYPSI_65816_ROOT)),)
+        $(error Please set CALYPSI_65816_ROOT in your environment!)
+    endif
 
-	CC             = cc65816
-	AS             = as65816
-	LD             = ln65816
-	TOOLCHAIN_ROOT = $(CALYPSI_65816_ROOT)
+    CC             = cc65816
+    AS             = as65816
+    LD             = ln65816
+    TOOLCHAIN_ROOT = $(CALYPSI_65816_ROOT)
 else
-	$(error "Unrecognized TOOLCHAIN: $(TOOLCHAIN)")
+    $(error Unrecognized TOOLCHAIN: "$(TOOLCHAIN)")
 endif
 
 SRC_DIR           = src