diff --git a/doc/tutorial_episode_8.pod b/doc/tutorial_episode_8.pod
index 1cc3a48..7cdd24e 100644
--- a/doc/tutorial_episode_8.pod
+++ b/doc/tutorial_episode_8.pod
@@ -38,7 +38,7 @@ that can be assigned to variables, you can have array literals. Below is the
 grammar rule for this:
 
  rule circumfix:sym<[ ]> {
-     '[' <EXPR> ** ',' ']'
+     '[' [<EXPR> ** ',']? ']'
  }
 
 Some examples are shown below:
@@ -60,7 +60,7 @@ constructed through a hashtable constructor. The syntax for this is expressed
 below:
 
  rule circumfix:sym<{ }> {
-     '{' <named_field> ** ',' '}'
+     '{' [<named_field> ** ',']? '}'
  }
 
  rule named_field {
diff --git a/src/Squaak/Grammar.pm b/src/Squaak/Grammar.pm
index 254b0ba..2d703c2 100644
--- a/src/Squaak/Grammar.pm
+++ b/src/Squaak/Grammar.pm
@@ -164,11 +164,11 @@ INIT {
 token circumfix:sym<( )> { '(' <.ws> <EXPR> ')' }
 
 rule circumfix:sym<[ ]> {
-    '[' <EXPR> ** ',' ']'
+    '[' [<EXPR> ** ',']? ']'
 }
 
 rule circumfix:sym<{ }> {
-    '{' <named_field> ** ',' '}'
+    '{' [<named_field> ** ',']? '}'
 }
 
 rule named_field {