diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index a9e207b..c1fc803 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -2842,7 +2842,7 @@
 to a data format
 
 ```
-SourceFile      = { attribute "," } [ PackageClause "," ] { ImportDecl "," } { Declaration "," } .
+SourceFile      = [ PackageClause "," ] { ImportDecl "," } { Declaration "," } .
 ```
 
 ```