diff --git a/src/pyj/read_book/annotations.pyj b/src/pyj/read_book/annotations.pyj
index e182eb59c7..a142b54f84 100644
--- a/src/pyj/read_book/annotations.pyj
+++ b/src/pyj/read_book/annotations.pyj
@@ -20,7 +20,7 @@ def highlight_get_cfi(hl):
     cfi = hl.start_cfi
     if cfi:
         si = f'/{hl.spine_index}' if hl.spine_index? else no_cfi
-        return f'{si}{cfi}'
+        return si + cfi
     return no_cfi