diff --git a/syntax/po.nanorc b/syntax/po.nanorc
index c9f0bccf..e3ecf5e2 100644
--- a/syntax/po.nanorc
+++ b/syntax/po.nanorc
@@ -27,3 +27,5 @@ color cyan "\\([abcefnrtv"\]|x[0-9abcdefABCDEF]{2}|[0-7]{3})"
 color brightwhite,yellow "\<(FIXME|TODO|XXX)\>"
 # Obsolete strings.
 color red "#~.*"
+# Stray control codes.
+color bold,pink,red "[[:cntrl:]]"