diff --git a/app/scodoc/gen_tables.py b/app/scodoc/gen_tables.py
index 72326132b..0a4b65ca7 100644
--- a/app/scodoc/gen_tables.py
+++ b/app/scodoc/gen_tables.py
@@ -63,12 +63,15 @@ from app.scodoc.sco_pdf import SU
 from app import log
 
 
-def mark_paras(L, tags):
-    """Put each (string) element of L between  <b>"""
+def mark_paras(L, tags) -> list[str]:
+    """Put each (string) element of L between  <tag>...</tag>,
+    for each supplied tag.
+    Leave non string elements untouched.
+    """
     for tag in tags:
-        b = "<" + tag + ">"
-        c = "</" + tag.split()[0] + ">"
-        L = [b + (x or "") + c for x in L]
+        start = "<" + tag + ">"
+        end = "</" + tag.split()[0] + ">"
+        L = [(start + (x or "") + end) if isinstance(x, str) else x for x in L]
     return L