diff --git a/ifd_builder.go b/ifd_builder.go
index 4854d6b..e28d67b 100644
--- a/ifd_builder.go
+++ b/ifd_builder.go
@@ -1126,6 +1126,9 @@ func (ib *IfdBuilder) AddTagsFromExisting(ifd *Ifd, itevr *IfdTagEntryValueResol
 				_, isUnknownUndefined := x.(TagUnknownType_UnknownValue)
 
 				if isUnknownUndefined == true {
+					// It's an undefined-type tag that we don't handle. If we
+					// don't know how to handle it, we can't know how many bytes
+					// it is and we must skip it.
 					continue
 				}
 
diff --git a/tags_unknown.go b/tags_unknown.go
index df53813..bf09ebe 100644
--- a/tags_unknown.go
+++ b/tags_unknown.go
@@ -390,6 +390,7 @@ func UndefinedValue(ifdPath string, tagId uint16, valueContext interface{}, byte
 	// Return encapsulated data rather than an error so that we can at least
 	// print/profile the opaque data.
 
+	// TODO(dustin): This won't ever work. The unit-count isn't necessarily correct. Revert to returning an error.
 	valueContextPtr.SetUnknownValueType(TypeByte)
 
 	valueBytes, err := valueContextPtr.ReadBytes()