diff --git a/src/environments/fancythm/fancythm.dtx b/src/environments/fancythm/fancythm.dtx
index 98fa61a..ab40892 100644
--- a/src/environments/fancythm/fancythm.dtx
+++ b/src/environments/fancythm/fancythm.dtx
@@ -237,10 +237,21 @@
 %       \cs{counter_alias:nn}\marg{counter_1}\marg{counter_2}
 %    \end{syntax}
 %		 
-%     
+%    Note that since 2022-06-02, the implementation of \cs{@counteralias}
+%    in \pkg{thmtools} has changed.
+%    Before, aliasing an already existing counter did not throw an error,
+%    which is considered a bug now
+%    (\href{https://github.com/muzimuzhi/thmtools/issues/28}{https://github.com/muzimuzhi/thmtools/issues/28}).
+%    Since \pkg{!!} relies on the old functionality,
+%    we adapt this here by undefining \cs{c@\meta{countername}} before calling
+%    \cs{@counteralias}.
 %
 %    \begin{macrocode}
-\cs_set_eq:Nc \counter_alias:nn { @counteralias }
+\cs_new:Npn \counter_alias:nn #1 % trailing #2
+  {
+    \cs_undefine:c { c@ #1 }
+    \use:c { @counteralias } { #1 } % implicit #2
+  }
 \cs_generate_variant:Nn \counter_alias:nn { n x }
 %    \end{macrocode}
 % \end{macro}