diff --git a/git-tools/hooks/commit-msg b/git-tools/hooks/commit-msg
index 52969670ca..b156d276df 100755
--- a/git-tools/hooks/commit-msg
+++ b/git-tools/hooks/commit-msg
@@ -12,6 +12,13 @@
 # ln -s ../../git-tools/hooks/commit-msg \\
 #   .git/hooks/commit-msg
 #
+# You can configure whether invalid commit messages abort commits:
+#
+# git config phpbb.hooks.commit-msg.fatal true	(abort)
+# git config phpbb.hooks.commit-msg.fatal false (warn only, do not abort)
+#
+# The default is to warn only.
+#
 # Warning/error messages use color by default if the output is a terminal
 # ("output" here is normally standard error when you run git commit).
 # To force or disable the use of color:
@@ -21,6 +28,15 @@
 
 config_ns="phpbb.hooks.commit-msg";
 
+if [ "$(git config --bool $config_ns.fatal)" = "true" ]
+then
+	fatal=1;
+	severity=Error;
+else
+	fatal=0;
+	severity=Warning;
+fi
+
 debug_level=$(git config --int $config_ns.debug || echo 0);
 
 # Error codes
@@ -47,9 +63,19 @@ debug()
 
 quit()
 {
-	# Now we always exit with success, since git will trash
-	# entered commit message if commit-msg hook exits with a failure.
-	exit 0
+	if [ $1 -eq 0 ] || [ $1 -eq $ERR_UNKNOWN ]
+	then
+		# success
+		exit 0;
+	elif [ $fatal -eq 0 ]
+	then
+		# problems found but fatal is false
+		complain 'Please run `git commit --amend` and fix the problems mentioned.' 1>&2
+		exit 0;
+	else
+		complain "Aborting commit." 1>&2
+		exit $1;
+	fi
 }
 
 use_color()
@@ -170,7 +196,7 @@ do
 					# Don't be too strict.
 					# Commits may be temporary, intended to be squashed later.
 					# Just issue a warning here.
-					complain "Warning: heading should be a sentence beginning with a capital letter." 1>&2
+					complain "$severity: heading should be a sentence beginning with a capital letter." 1>&2
 					complain "You entered:" 1>&2
 					complain "$line" 1>&2
 				fi