diff --git a/grammar/src/expressions.grm b/grammar/src/expressions.grm
index 01942310760..e34c2bc04c1 100644
--- a/grammar/src/expressions.grm
+++ b/grammar/src/expressions.grm
@@ -89,7 +89,7 @@ binaryOperation // Decreasing precedence
 
 assignmentOperator
   : "="
-  : "+=" : "-=" : "*=" : "/=" // TODO: |=, %= and <<= make more sense than |, % or << alone, and so for others
+  : "+=" : "-=" : "*=" : "/=" : "%="// TODO: |=, %= and <<= make more sense than |, % or << alone, and so for others
   ;
 
 assignment
diff --git a/grammar/src/lexical.grm b/grammar/src/lexical.grm
index a911b6817d3..7fb845d6116 100644
--- a/grammar/src/lexical.grm
+++ b/grammar/src/lexical.grm
@@ -19,7 +19,7 @@ NoEscapeString : /* """-quoted string */;
 <= >= == != === !==
 + - * / %
 =
-+= -= *= /=
++= -= *= /= %=
 ++ -- !
 && ||  -- may be just & and |
 =>