ANTLR No viable alternative at input query - antlr

Question

I am designing a parser for a small language - the grammar I have is as follows:
grammar Test;
r : specification+;
specification : MODULE module_def EOF;
module_def : ID EQ classExp;
classExp : basicClassExp
| altClassExp
;
basicClassExp : CLASS (classCode)* END;
altClassExp : ALTCLASS (classCode)* END;
classCode : 'classCode';
EXCLAMATION : '!';
EQ : '=';
MODULE : 'module';
END : 'end';
CLASS : 'class';
ALTCLASS : 'altclass';
ID
: JavaLetter JavaLetterOrDigit*
;
fragment
JavaLetter
: [a-zA-Z$_]
| ~[\u0000-\u007F\uD800-\uDBFF]
| [\uD800-\uDBFF] [\uDC00-\uDFFF]
;
fragment
JavaLetterOrDigit
: [a-zA-Z0-9$_]
| ~[\u0000-\u007F\uD800-\uDBFF]
| [\uD800-\uDBFF] [\uDC00-\uDFFF]
;
WS : [ \t\r\n\u000C]+ -> skip
;
COMMENT
: '/*' .*? '*/' -> channel(HIDDEN)
;
LINE_COMMENT
: '//' ~[\r\n]* -> channel(HIDDEN)
;
An example of correct code would be:
module T = class end
When I run it on the following code :
module ! T ! = !
class !
end !
I expect it to report errors where the exclamation marks are. Instead I get:
line 1:7 extraneous input '!' expecting ID
line 1:11 extraneous input '!' expecting '='
line 1:15 no viable alternative at input '!'
When I remove the altClassExp rule alternative, it reports all errors i.e.
line 1:7 extraneous input '!' expecting ID
line 1:11 extraneous input '!' expecting '='
line 1:15 extraneous input '!' expecting 'class'
line 2:10 extraneous input '!' expecting {'classCode', 'end'}
line 3:6 extraneous input '!' expecting <EOF>
What do I need to change so I can keep my altClassExp rule and also report all the extraneous exclamation marks?
Thanks