diff --git a/setup/dkim.sh b/setup/dkim.sh
index 9097e452..b4969ec3 100755
--- a/setup/dkim.sh
+++ b/setup/dkim.sh
@@ -63,9 +63,13 @@ if [ ! -f "$STORAGE_ROOT/mail/dkim/mail.key" ]; then
 	
 	# Change format from pkcs#8 to pkcs#1, dkimpy seemingly is not able to handle the #8 format
 	# See bug https://bugs.launchpad.net/dkimpy/+bug/1978835
-	openssl pkey -in $STORAGE_ROOT/mail/dkim/mail.key -traditional -out $STORAGE_ROOT/mail/dkim/mail.key.1
-	mv -f $STORAGE_ROOT/mail/dkim/mail.key $STORAGE_ROOT/mail/dkim/mail.key.8
-	cp -f $STORAGE_ROOT/mail/dkim/mail.key.1 $STORAGE_ROOT/mail/dkim/mail.key
+	line=$(head -n 1 mail.key)
+	if [ ! "$line" = "-----BEGIN RSA PRIVATE KEY-----" ]; then
+		# Generate pkcs#1 key from the pkcs#8 key
+		openssl pkey -in $STORAGE_ROOT/mail/dkim/mail.key -traditional -out $STORAGE_ROOT/mail/dkim/mail.key.1
+		mv -f $STORAGE_ROOT/mail/dkim/mail.key $STORAGE_ROOT/mail/dkim/mail.key.8
+		cp -f $STORAGE_ROOT/mail/dkim/mail.key.1 $STORAGE_ROOT/mail/dkim/mail.key
+	fi
 fi
 
 if [ ! -f "$STORAGE_ROOT/mail/dkim/box-ed25519.key" ]; then