diff --git a/docs/grammar.txt b/docs/grammar.txt
index c67a8a4a2..f03502395 100644
--- a/docs/grammar.txt
+++ b/docs/grammar.txt
@@ -7,7 +7,7 @@ ImportDirective = 'import' StringLiteral ('as' Identifier)? ';'
         | 'import' ('*' | Identifier) ('as' Identifier)? 'from' StringLiteral ';'
         | 'import' '{' Identifier ('as' Identifier)? ( ',' Identifier ('as' Identifier)? )* '}' 'from' StringLiteral ';'
 
-ContractDefinition = ( 'contract' | 'library' ) Identifier
+ContractDefinition = ( 'contract' | 'library' | 'interface' ) Identifier
                      ( 'is' InheritanceSpecifier (',' InheritanceSpecifier )* )?
                      '{' ContractPart* '}'