diff --git a/S05-mass/charsets.t b/S05-mass/charsets.t
index 1648d8591d..422c68bdc2 100644
--- a/S05-mass/charsets.t
+++ b/S05-mass/charsets.t
@@ -4,7 +4,7 @@ use Test;
 
 # L<S05/Extensible metasyntax (C<< <...> >>)/"The special named assertions include">
 
-plan 16;
+plan 17;
 
 #?niecza skip 'Tests not completing under niecza'
 {
@@ -48,3 +48,9 @@ plan 16;
     is $latin-chars.comb(/<+ :HexDigit - lower >/).join, "0123456789ABCDEF", 'combined unicode and builtins';
 
 }
+
+# RT #121365
+{
+    'o' ~~ /<:!Upper>*/;
+    is ~$/, 'o', 'Can match negated quantified character class';
+}