diff --git a/test/mri/excludes/TestRegexp.rb b/test/mri/excludes/TestRegexp.rb
index fb31614bfea..457ce918288 100644
--- a/test/mri/excludes/TestRegexp.rb
+++ b/test/mri/excludes/TestRegexp.rb
@@ -15,7 +15,7 @@
 exclude :test_matchdata, "<42> expected but was <nil>."
 exclude :test_named_capture, "<\"#<MatchData \\\"&amp; y\\\" foo:\\\"amp\\\" foo:\\\"y\\\">\"> expected but was <\"#<MatchData \\\"&amp; y\\\" foo:\\\"amp\\\" 2:\\\"y\\\">\">."
 exclude :test_named_capture_nonascii, "IndexError expected but nothing was raised."
-exclude :test_once_multithread, "TypeError: TruffleRuby doesn't have a case for the org.truffleruby.core.array.ArrayAppendOneNodeGen node with values of type Array(org.truffleruby.core.array.RubyArray)[org.truffleruby.core.array.library.SharedArrayStorage,1] org.truffleruby.core.regexp.RubyRegexp"
+exclude :test_once_multithread, "transient(fails on CI): <[/1/, /1/]> expected but was <[/1/]>."
 exclude :test_parse, "Polyglot::ForeignException: invalid group reference 80"
 exclude :test_parse_kg, "Polyglot::ForeignException: undefined name <-1> reference"
 exclude :test_posix_bracket, "expected: /duplicated range/"
diff --git a/test/mri/failing.exclude b/test/mri/failing.exclude
index b69fc9aac08..8c3b194e9d8 100644
--- a/test/mri/failing.exclude
+++ b/test/mri/failing.exclude
@@ -1,8 +1,11 @@
 # Explicitly unsupported
 
-ruby/test_ast.rb
+ruby/test_ast.rb # tests RubyVM::InstructionSequence
+ruby/test_compile_prism.rb # tests RubyVM::InstructionSequence
+ruby/test_iseq.rb # tests RubyVM::InstructionSequence
 ruby/test_mjit.rb
 ruby/test_mjit_debug.rb
+ruby/test_rubyvm.rb # tests RubyVM
 dbm/test_dbm.rb
 gdbm/test_gdbm.rb
 test_pty.rb
@@ -75,8 +78,4 @@ dtrace/test_singleton_function.rb
 dtrace/test_string.rb
 misc/test_ruby_mode.rb
 ruby/enc/test_windows_1251.rb
-ruby/test_ast.rb # tests RubyVM::InstructionSequence
-ruby/test_compile_prism.rb # tests RubyVM::InstructionSequence
-ruby/test_iseq.rb # RubyVM
-ruby/test_rubyvm.rb
 ruby/test_bignum.rb # relies on Bignums on Fixnum range
diff --git a/tool/parse_mri_errors.rb b/tool/parse_mri_errors.rb
index ed801ad8206..9d190115a19 100755
--- a/tool/parse_mri_errors.rb
+++ b/tool/parse_mri_errors.rb
@@ -410,6 +410,16 @@ def process_test_failures!(contents)
     error_display = error_lines[index]
 
     # Mismatched expectations span two lines. It's much more useful if they're combined into one message.
+    #
+    # FIXME: A line with "expected but was" may be prefixed with additional line, e.g.
+    # ```
+    #   1) Failure:
+    # Test_SPrintf#test_format_integer(% #-020.d) [/b/b/e/main/test/mri/tests/cext-ruby/test_printf.rb:153]:
+    # rb_sprintf("% #-020.d", 2147483647).
+    # <[" 2147483647         ", "% #-020.d"]> expected but was
+    # <[" 0000000002147483647", "% #-020.d"]>.
+    # ```
+    # In this case only the first line of the message is added to the result - 'rb_sprintf("% #-020.d", 2147483647).'
     if error_display =~ /expected but was/
       index += 1
       error_display << ' ' + error_lines[index]