diff --git a/doc/bugs/whereused_false_match_on_longer_key.mdwn b/doc/bugs/whereused_false_match_on_longer_key.mdwn
new file mode 100644
index 0000000000..30a5f0ef36
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+++ b/doc/bugs/whereused_false_match_on_longer_key.mdwn
@@ -0,0 +1,7 @@
+It's possible for `git annex whereused --key=foo` to find a match in a
+file that uses key "foobar".
+
+One way this is likely to happen is SHA256 keys with and without extension,
+for the same content. Or WORM keys with similar filenames.
+
+--[[Joey]]