diff --git a/convert.py b/convert.py
index 2e832ef..e968d68 100644
--- a/convert.py
+++ b/convert.py
@@ -45,7 +45,7 @@
 # Patterns tried in order; first match wins
 _SLUG_PATTERNS: list[tuple[str, re.Pattern]] = [
     # PublicationName-YYYY-MM[...].pdf  →  YYYY-MM
-    ("year-month", re.compile(r".*?[_-](\d{4})[_-](\d{2})(?:[_-]|\.|$)", re.IGNORECASE)),
+    ("year-month", re.compile(r".*?[ _-](\d{4})[_-](\d{2})(?:[_-]|\.|$)", re.IGNORECASE)),
     # Vol-N or Volume-N  →  vol-N  (bare V excluded: too ambiguous, e.g. _v2 meaning version 2)
     ("volume", re.compile(r"(?:Vol(?:ume)?)[_\-\.\s]?(\d+)", re.IGNORECASE)),
     # No-N or Issue-N  →  no-N