diff --git a/Programs/makefile b/Programs/makefile
index 636bd5f..fd01eec 100644
--- a/Programs/makefile
+++ b/Programs/makefile
@@ -76,7 +76,7 @@ cosmos: $(COSMOS) $(APPS)
 $(COSMOS_DISK): $(APPS)
 	@mkdir -p $(@D)
 	rm -f $@
-	$(DISKTOOL) format $@ 256 2
+	$(DISKTOOL) format $@ 2048 4
 	@for app in $(APPS); do $(DISKTOOL) put $@ $$app; done
 
 # The system as well as the disk. Building only the image leaves whatever cosmos.bin was
diff --git a/Tests/makedisks.sh b/Tests/makedisks.sh
index 5ee3542..10da6a4 100755
--- a/Tests/makedisks.sh
+++ b/Tests/makedisks.sh
@@ -59,7 +59,11 @@ for i in 1 2 3 4 5 6 7 8; do "$TOOL" put "$DISKS/sbfs.img" "filler$i.txt" >/dev/
 # to the hardware, so something has to check that one still gives the machine back.
 #
 # notes.txt is there so that loading something that is not a program can be tried too.
-"$TOOL" format "$DISKS/cosmos.img" 256 2 >/dev/null
+# 512K, and four directory blocks for 32 files. It was 64K and 16, which was ample for a
+# disk that held programs and nothing else - but the native assembler reads SOURCE from
+# here, and the CosmOS sources alone are 104,142 bytes against the 65,536 a 256 block disk
+# holds. A machine that is going to assemble itself has to be able to hold its own source.
+"$TOOL" format "$DISKS/cosmos.img" 2048 4 >/dev/null
 "$ROOT/Assembler" -I "$ROOT/Programs/CosmOS/Source" \
     "$ROOT/Programs/CosmOS/Apps/greet.asm" -o "$WORK/greet.sbx" >/dev/null
 "$TOOL" put "$DISKS/cosmos.img" "$WORK/greet.sbx" >/dev/null