diff --git a/tests/scripts/check_files.py b/tests/scripts/check_files.py
index d20ec2e9ec..352b55eaa8 100755
--- a/tests/scripts/check_files.py
+++ b/tests/scripts/check_files.py
@@ -268,7 +268,7 @@ class UnicodeIssueTracker(LineIssueTracker):
 
     heading = "Invalid UTF-8 or forbidden character:"
 
-    # Only allow valid UTF-8, and only white-listed characters.
+    # Only allow valid UTF-8, and only other explicitly allowed characters.
     # We deliberately exclude all characters that aren't a simple non-blank,
     # non-zero-width glyph, apart from a very small set (tab, ordinary space,
     # line breaks, "basic" no-break space and soft hyphen). In particular,
@@ -285,6 +285,7 @@ class UnicodeIssueTracker(LineIssueTracker):
         '\u2070\u2071\u2074-\u208E\u2090-\u209C', # Superscripts and Subscripts
         '\u2190-\u21FF', # Arrows
         '\u2200-\u22FF', # Mathematical Symbols
+        '\u2500-\u257F' # Box Drawings characters used in markdown trees
     ])
     # Allow any of the characters and ranges above, and anything classified
     # as a word constituent.