diff --git a/doc/porting_guide.txt b/doc/porting_guide.txt
index 0511c143b..e92d75a55 100644
--- a/doc/porting_guide.txt
+++ b/doc/porting_guide.txt
@@ -232,7 +232,7 @@ The DosBox port can now be prepared by executing
 
 However, we get the following error message:
 
-  Error: <rep-dir>/ports/dosbox.port is out of date, expected <fingerprint>
+! Error: <rep-dir>/ports/dosbox.port is out of date, expected <fingerprint>
 
 We get this message because we had specified the "dummy" hash value in
 the _dosbox.hash_ file. The prepare_port tool computes a fingerprint