diff --git a/dfimagetools/definitions.py b/dfimagetools/definitions.py
index bc72fc2..7e2188d 100644
--- a/dfimagetools/definitions.py
+++ b/dfimagetools/definitions.py
@@ -17,5 +17,19 @@
 NON_PRINTABLE_CHARACTERS.update({
     value: f'\\U{value:08x}' for value in range(0xd800, 0xe000)})
 
+# Escape undefined Unicode characters as \U########
+NON_PRINTABLE_CHARACTERS.update({value: f'\\U{value:08x}' for value in (
+    0xfdd0, 0xfdd1, 0xfdd2, 0xfdd3, 0xfdd4, 0xfdd5, 0xfdd6, 0xfdd7, 0xfdd8,
+    0xfdd9, 0xfdda, 0xfddb, 0xfddc, 0xfddd, 0xfdde, 0xfddf, 0xfffe, 0xffff,
+    0x1fffe, 0x1ffff, 0x2fffe, 0x2ffff, 0x3fffe, 0x3ffff, 0x4fffe, 0x4ffff,
+    0x5fffe, 0x5ffff, 0x6fffe, 0x6ffff, 0x7fffe, 0x7ffff, 0x8fffe, 0x8ffff,
+    0x9fffe, 0x9ffff, 0xafffe, 0xaffff, 0xbfffe, 0xbffff, 0xcfffe, 0xcffff,
+    0xdfffe, 0xdffff, 0xefffe, 0xeffff, 0xffffe, 0xfffff, 0x10fffe,
+    0x10ffff)})
+
+# Escape observed non-printable Unicode characters as \U########
+NON_PRINTABLE_CHARACTERS.update({value: f'\\U{value:08x}' for value in (
+    0x2028, 0x2029, 0xe000, 0xf8ff, 0xf0000, 0xffffd, 0x100000, 0x10fffd)})
+
 NON_PRINTABLE_CHARACTER_TRANSLATION_TABLE = str.maketrans(
     NON_PRINTABLE_CHARACTERS)