https://github.com/Perl/perl5/issues/22353#issuecomment-2198256977

diff -Nurp a/typemap b/typemap
--- a/typemap	2025-05-07 18:15:00.715697457 -0500
+++ b/typemap	2025-05-07 18:17:18.381278764 -0500
@@ -37,9 +37,9 @@ T_LOOP
 
 T_WATCHER
 	if (!(SvROK ($arg) && SvOBJECT (SvRV ($arg))
-              && (SvSTASH (SvRV ($arg)) == stash_${ \($type =~ /ev_(\S+)/, \"$1\") }
-                  || sv_derived_from ($arg, \"EV::${ \($type =~ /ev_(\S+)/, ucfirst \"$1\") }\"))))
-          croak (\"object is not of type EV::${ \($type =~ /ev_(\S+)/, ucfirst \"$1\") }\");
+              && (SvSTASH (SvRV ($arg)) == stash_${ ($type =~ /ev_(\S+)/, \qq{$1}) }
+                  || sv_derived_from ($arg, \"EV::${ ($type =~ /ev_(\S+)/, \ucfirst qq{$1}) }\"))))
+          croak (\"object is not of type EV::${ ($type =~ /ev_(\S+)/, \ucfirst qq{$1}) }\");
 	$var = ($type)SvPVX (SvRV ($arg));
 
 OUTPUT