diff --git a/content.go b/content.go
index 3eafde5..048e57a 100644
--- a/content.go
+++ b/content.go
@@ -21,13 +21,22 @@ type Content interface {
 func NewContent(contentType int, mediaType string, content any) Content {
 	switch contentType {
 	case 0:
-		return newInlineTextContent(mediaType, content.(string))
+		if stringContent, ok := content.(string); ok {
+			return newInlineTextContent(mediaType, stringContent)
+		}
+		return nil
 	case 1:
-		return newInlineXHTMLContent(mediaType, content.(*XHTMLDiv))
+		if xhtmlDivContent, ok := content.(*XHTMLDiv); ok {
+			return newInlineXHTMLContent(mediaType, xhtmlDivContent)
+		}
+		return nil
 	case 2:
 		return newInlineOtherContent(mediaType, content)
 	case 3:
-		return newOutOfLineContent(mediaType, content.(string))
+		if stringContent, ok := content.(string); ok {
+			return newOutOfLineContent(mediaType, stringContent)
+		}
+		return nil
 	default:
 		return nil
 	}