diff --git a/recipes/sms/Makefile b/recipes/sms/Makefile
index f3d661c..3910b2d 100644
--- a/recipes/sms/Makefile
+++ b/recipes/sms/Makefile
@@ -2,6 +2,7 @@ TARGET = os.bin
 BASE = ../../
 STAGE = $(BASE)/cvm/stage
 BLKPACK = $(BASE)/tools/blkpack
+SMSROM = $(BASE)/tools/smsrom
 EMUL = $(BASE)/emul/hw/sms/sms
 
 .PHONY: all
@@ -9,6 +10,7 @@ all: $(TARGET)
 $(TARGET): xcomp.fs $(STAGE) blkfs
 	cat xcomp.fs | $(STAGE) blkfs > $@
 
+$(SMSROM):
 $(BLKPACK):
 	$(MAKE) -C ../tools
 
@@ -18,8 +20,8 @@ blkfs: $(BLKPACK)
 $(STAGE):
 	$(MAKE) -C $(BASE)/cvm stage
 
-os.sms: $(TARGET) $(STAGE)
-	dd if=$(TARGET) bs=32752 conv=sync | cat - sega.bin > $@
+os.sms: $(TARGET) $(STAGE) $(SMSROM)
+	$(SMSROM) $(TARGET) > $@
 
 $(EMUL):
 	$(MAKE) -C ${@:%/sms=%}
diff --git a/recipes/sms/sega.bin b/recipes/sms/sega.bin
deleted file mode 100644
index 9db7c7c..0000000
Binary files a/recipes/sms/sega.bin and /dev/null differ
diff --git a/tools/.gitignore b/tools/.gitignore
index f8ae9ea..a335747 100644
--- a/tools/.gitignore
+++ b/tools/.gitignore
@@ -1,13 +1,10 @@
 /memdump
 /blkdump
 /upload
-/fontcompile
 /ttysafe
 /pingpong
-/slatest
-/stripfc
-/bin2c
 /exec
 /blkpack
 /blkunpack
 /blkup
+/smsrom
diff --git a/tools/Makefile b/tools/Makefile
index 853a681..063ac7b 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -6,9 +6,10 @@ EXEC_TGT = exec
 BLKPACK_TGT = blkpack
 BLKUNPACK_TGT = blkunpack
 BLKUP_TGT = blkup
+SMSROM_TGT = smsrom
 TARGETS = $(MEMDUMP_TGT) $(UPLOAD_TGT) \
 	$(TTYSAFE_TGT) $(PINGPONG_TGT) $(EXEC_TGT) $(BLKPACK_TGT) \
-    $(BLKUNPACK_TGT) $(BLKUP_TGT)
+    $(BLKUNPACK_TGT) $(BLKUP_TGT) $(SMSROM_TGT)
 OBJS = common.o
 
 all: $(TARGETS)
@@ -25,6 +26,7 @@ $(EXEC_TGT): $(EXEC_TGT).c
 $(BLKPACK_TGT): $(BLKPACK_TGT).c
 $(BLKUNPACK_TGT): $(BLKUNPACK_TGT).c
 $(BLKUP_TGT): $(BLKUP_TGT).c
+$(SMSROM_TGT): $(SMSROM_TGT).c
 $(TARGETS): $(OBJS)
 	$(CC) $(CFLAGS) $@.c $(OBJS) -o $@
 
diff --git a/tools/smsrom.c b/tools/smsrom.c
new file mode 100644
index 0000000..77136d0
--- /dev/null
+++ b/tools/smsrom.c
@@ -0,0 +1,53 @@
+/* ./smsrom fname
+
+Transforms binary at fname into an 8K, 16K or 32K Sega Master System ROM with
+a header fit for an Export SMS. The resulting ROM is spit to stdout.
+
+Whether the ROM is 8, 16 or 32K depends on the size of binary at fname.
+*/
+#include <stdio.h>
+#include <inttypes.h>
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./smsrom fname\n");
+        return 1;
+    }
+    FILE *fp = fopen(argv[1], "r");
+    if (!fp) {
+        fprintf(stderr, "Can't open %s.\n", argv[1]);
+        return 1;
+    }
+    fseek(fp, 0, SEEK_END);
+    long fsize = ftell(fp);
+    fseek(fp, 0, SEEK_SET);
+    uint8_t hdsz = 0x4a; // size flag in header. either 4a, 4b or 4c.
+    int romsize = 0x2000;
+    while (romsize-16 < fsize) {
+        romsize *= 2;
+        hdsz++;
+        if (romsize > 0x8000) {
+            fprintf(stderr, "binary too big\n");
+            return 1;
+        }
+    }
+    uint16_t chksum = 0;
+    for (int i=0; i<romsize-16; i++) {
+        int c = getc(fp);
+        if (c == EOF) c = 0;
+        putchar(c);
+        chksum += c;
+    }
+    // and now, the header
+    printf("TMR SEGA");
+    putchar(0);
+    putchar(0);
+    putchar(chksum & 0xff);
+    putchar(chksum >> 8);
+    putchar(0);
+    putchar(0);
+    putchar(0);
+    putchar(hdsz);
+    return 0;
+}