diff --git a/src/docx/opc/oxml.py b/src/docx/opc/oxml.py
index 7d3c489d6..ba28dcf84 100644
--- a/src/docx/opc/oxml.py
+++ b/src/docx/opc/oxml.py
@@ -175,6 +175,8 @@ def target_mode(self):
 
         Defaults to ``Internal``.
         """
+        if self.target_ref and self.target_ref.startswith("#"):
+            return RTM.EXTERNAL
         return self.get("TargetMode", RTM.INTERNAL)