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diff --git a/README.md b/README.md
index 32154a4..eec937b 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,10 @@ Entries in this repository also uses the following non-standard BibTeX fields:
 
 * `ddc`: Dewey Decimal Classification - https://en.wikipedia.org/wiki/Dewey_Decimal_Classification.
 
+* `lcc`: Library of Congress Classification - https://en.wikipedia.org/wiki/Library_of_Congress_Classification
+
+* `lccn`: Library of Congress Control Number - https://en.wikipedia.org/wiki/Library_of_Congress_Control_Number
+
 ## Testing
 
     sudo apt install make biber pybtex