diff --git a/DeDRM_plugin/ion.py b/DeDRM_plugin/ion.py
index 3eeef3c..d8d52aa 100644
--- a/DeDRM_plugin/ion.py
+++ b/DeDRM_plugin/ion.py
@@ -512,6 +512,8 @@ class BinaryIonParser(object):
 
         if table is not None:
             self.symbols.import_(table, min(maxid, len(table.symnames)))
+            if len(table.symnames) < maxid:
+                self.symbols.importunknown(name + "-unknown", maxid - len(table.symnames))
         else:
             self.symbols.importunknown(name, maxid)