diff --git a/bibtexparser/library.py b/bibtexparser/library.py
index dfadc9c..c19e144 100644
--- a/bibtexparser/library.py
+++ b/bibtexparser/library.py
@@ -196,7 +196,7 @@ def strings(self) -> List[String]:
     @property
     def strings_dict(self) -> Dict[str, String]:
         """Dict representation of all @string blocks in the library."""
-        return self._strings_by_key
+        return self._strings_by_key.copy()
 
     @property
     def entries(self) -> List[Entry]: