diff --git a/offlineu_core.py b/offlineu_core.py
index 7305fd3..4117d8e 100644
--- a/offlineu_core.py
+++ b/offlineu_core.py
@@ -526,7 +526,10 @@ def find_course_thumbnail(course_path: str) -> Optional[str]:
 
 
 _SECTION_NAME_RE = re.compile(
-    r'^(section|module|chapter|part|unit|lesson)\b|^\d+[\s_.\-]', re.IGNORECASE
+    # (?![a-z]) rather than \b after the keyword - \b won't fire between
+    # "Chapter" and an immediately-following "_" since underscore counts
+    # as a word character too (e.g. "Chapter_1-Introduction").
+    r'^(section|module|chapter|part|unit|lesson)(?![a-z])|^\d+[\s_.\-]', re.IGNORECASE
 )