diff --git a/entry.go b/entry.go
index 57411d1..f1f3713 100644
--- a/entry.go
+++ b/entry.go
@@ -213,7 +213,7 @@ func (e *Entry) Check() error {
 		// is not an XML media type [RFC3023], does not begin with "text/", and
 		// does not end with "/xml" or "+xml".
 		mediaType := e.Content.getType()
-		if !isXMLMediaType(mediaType) && !strings.HasPrefix(mediaType, "text/") {
+		if isValidMediaType(mediaType) && !isXMLMediaType(mediaType) && !strings.HasPrefix(mediaType, "text/") {
 			return fmt.Errorf("no summary element of entry %v but media type not xml", e.ID.URI)
 		}
 	}