Index: src/Parser/parser.yy
===================================================================
--- src/Parser/parser.yy	(revision 1a73dbb6911a9809536835bd2e8a1354073630e7)
+++ src/Parser/parser.yy	(revision bf205679e365ce7db05a5c24d237c676a256dbb3)
@@ -10,6 +10,6 @@
 // Created On       : Sat Sep  1 20:22:55 2001
 // Last Modified By : Peter A. Buhr
-// Last Modified On : Fri Feb 24 14:46:55 2023
-// Update Count     : 5983
+// Last Modified On : Sat Feb 25 09:52:06 2023
+// Update Count     : 5986
 //
 
@@ -1173,6 +1173,4 @@
 	comma_expression_opt ';'
 		{ $$ = new StatementNode( build_expr( $1 ) ); }
-	| MUTEX '(' ')' comma_expression ';'
-		{ $$ = new StatementNode( build_mutex( nullptr, new StatementNode( build_expr( $4 ) ) ) ); }
 	;
 
@@ -1584,8 +1582,11 @@
 	;
 
-// If MUTEX becomes a general qualifier, there are shift/reduce conflicts, so change syntax to "with mutex".
+// If MUTEX becomes a general qualifier, there are shift/reduce conflicts, so possibly change syntax to "with mutex".
 mutex_statement:
-	MUTEX '(' argument_expression_list ')' statement
-		{ $$ = new StatementNode( build_mutex( $3, $5 ) ); }
+	MUTEX '(' argument_expression_list_opt ')' statement
+		{
+			if ( ! $3 ) { SemanticError( yylloc, "mutex argument list cannot be empty." ); $$ = nullptr; }
+			$$ = new StatementNode( build_mutex( $3, $5 ) );
+		}
 	;