diff --git a/scanner/context.go b/scanner/context.go
index 9e3e69b..2ca1a13 100644
--- a/scanner/context.go
+++ b/scanner/context.go
@@ -1,7 +1,7 @@
 package scanner
 
 import (
-	"fmt"
+	"errors"
 	"strconv"
 	"strings"
 	"sync"
@@ -137,7 +137,7 @@ func (c *Context) validateDocumentLineIndentAfterSpaceOnly(column int) error {
 		return nil
 	}
 	if c.docSpaceOnlyIndentColumn > column {
-		return fmt.Errorf("invalid number of indent is specified after space only")
+		return errors.New("invalid number of indent is specified after space only")
 	}
 	return nil
 }
@@ -147,7 +147,7 @@ func (c *Context) validateDocumentLineIndentColumn() error {
 		return nil
 	}
 	if c.docFirstLineIndentColumn > c.docLineIndentColumn {
-		return fmt.Errorf("invalid number of indent is specified in the document header")
+		return errors.New("invalid number of indent is specified in the document header")
 	}
 	return nil
 }