diff --git a/README.md b/README.md
index a7cc7ff..fb4114f 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,8 @@ This package converts the Shape Expression Compact (ShExC) into Python JSON Sche
 ```bash
 > pip install PyShExC
 ```
+You will also need the `shexSpec/grammar` repository. This contains the file `ShExDoc.g4`
+which is used to initialize the parser.
 
 ## Usage
 
@@ -219,4 +221,4 @@ optional arguments:
 
 [] a shex:Schema ;
     shex:shapes <http://a.example/S1> .
-```
\ No newline at end of file
+```