diff --git a/example-os/.gitignore b/example-os/.gitignore
index bf41a39..96a543c 100644
--- a/example-os/.gitignore
+++ b/example-os/.gitignore
@@ -1,4 +1,5 @@
 /os.sh
 /os.ndisasm.disasm
 /os.reasm.asm
-/os.reasm
\ No newline at end of file
+/os.reasm
+/os.reasm.disasm
\ No newline at end of file
diff --git a/example-os/Makefile b/example-os/Makefile
index 5b4e11c..097a82a 100644
--- a/example-os/Makefile
+++ b/example-os/Makefile
@@ -9,14 +9,7 @@ os.sh: os.asm ../deploy-screenshots Makefile
 	chmod a+x $@
 
 os.ndisasm.disasm: os.sh Makefile
-	(echo "[BITS 16]"; \
-	 echo "[ORG 0x7c00]"; \
-	 ndisasm -o 0x7C00 $< \
-         | uniq -s 8 -c \
-         | sed -r -e 's/\s*1 //; t; s/\s*([0-9]+) ([^ ]+\s+[^ ]+\s+)/\2times \1 /' \
-         | sed -r -e 's/([^ ]+\s+[0-9A-F]{4}\s+jz) 0x/\1 short 0x/') > $@
-#         The last sed line just above fixes an issue with ndisasm
-#         (it fails to annotate the jz with short).
+	../utils/compact-ndisasm.sh $< $@
 
 os.reasm.asm: os.ndisasm.disasm Makefile
 	sed -r -e 's/^[^ ]+ +[^ ]+ +//' $< > $@
@@ -26,7 +19,9 @@ os.reasm: os.reasm.asm os.sh Makefile
 	@echo "diff $@ os.sh"
 	@diff $@ os.sh \
          && echo "Re-assembled file is identical to os.sh" \
-         || (echo "Re-assembled file is different from os.sh"; exit 1)
+         || (../utils/compact-ndisasm.sh $@ os.reasm.disasm; \
+	     echo "Re-assembled file is different from os.sh. Use meld os.ndisasm.disasm os.reasm.disasm to see differences."; \
+	     exit 1)
 
 .PHONY: clean Makefile
 clean:
diff --git a/utils/compact-ndisasm.sh b/utils/compact-ndisasm.sh
new file mode 100755
index 0000000..dcb52e4
--- /dev/null
+++ b/utils/compact-ndisasm.sh
@@ -0,0 +1,16 @@
+in=$1
+out=$2
+
+# Add -s 0x1234 to te ndisasm command-line to specify that there is an
+# instruction starting at 0x1234. Use this when ndisasm misinterprets
+# some instructions due to db.
+skip=""
+for i in `seq 0 255`; do skip="$skip -s 0x7e$(printf %02x $i)"; done
+(echo "[BITS 16]"; \
+ echo "[ORG 0x7c00]"; \
+ ndisasm -s 0x7c78 $skip -o 0x7C00 "$in" \
+ | uniq -s 8 -c \
+ | sed -r -e 's/^\s*1 //; t; s/^\s*([0-9]+) ([^ ]+\s+[^ ]+\s+)/\2times \1 /' \
+ | sed -r -e 's/([^ ]+\s+[0-9A-F]{4}\s+j[^ ]+ )0x/\1short 0x/') > "$out"
+# The last sed line just above fixes an issue with ndisasm
+# (it fails to annotate jz and jnc (and possibly other) with short).