diff --git a/parser.go b/parser.go
index 5c23171..2859b65 100644
--- a/parser.go
+++ b/parser.go
@@ -444,8 +444,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 			} else if tk.IsSymbol(SymStar) {
 				tk.SetSymbol(SymDereference)
 			} else if tk.IsSymbol(SymExclamation) {
-				err = tk.Errorf("postfix opertor %q requires an operand on its left side", tk)
-				break
+				tk.SetSymbol(SymNot)
 			}
 			firstToken = false
 		}
diff --git a/t_bool_test.go b/t_bool_test.go
index 6997352..c864fd0 100644
--- a/t_bool_test.go
+++ b/t_bool_test.go
@@ -26,12 +26,13 @@ func TestBool(t *testing.T) {
 		/*  12 */ {`true or false`, true, nil},
 		/*  13 */ {`true or []`, true, nil},
 		/*  14 */ {`[] or false`, nil, errors.New(`got list as left operand type of 'OR' operator, it must be bool`)},
+		/*  15 */ {`!true`, false, nil},
 		/*  13 */ //{`true or []`, nil, errors.New(`[1:8] left operand 'true' [bool] and right operand '[]' [list] are not compatible with operator "OR"`)},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
-	// runTestSuiteSpec(t, section, inputs, 1)
+	// runTestSuiteSpec(t, section, inputs, 15)
 	runTestSuite(t, section, inputs)
 }