diff --git a/src/mkdocs_bibtex/registry.py b/src/mkdocs_bibtex/registry.py
index 21aae23..d4e87ae 100644
--- a/src/mkdocs_bibtex/registry.py
+++ b/src/mkdocs_bibtex/registry.py
@@ -85,8 +85,8 @@ def __init__(self, bib_files: list[str], csl_file: str):
             raise ValueError("Pandoc version 2.11 or higher is required for this registry")
 
         # Cache for formatted citations
-        self._inline_cache = {}
-        self._reference_cache = {}
+        self._inline_cache: dict[str, str] = {}
+        self._reference_cache: dict[str, str] = {}
 
     def inline_text(self, citation_block: CitationBlock) -> str:
         """Returns cached inline citation text"""