diff -Nurd fish-3.7.1/src/fish_tests.cpp fish-3.7.1.new/src/fish_tests.cpp
--- fish-3.7.1/src/fish_tests.cpp       2024-03-18 20:40:45.000000000 -0700
+++ fish-3.7.1.new/src/fish_tests.cpp   2025-08-11 02:17:54.184887104 -0700
@@ -7009,7 +7009,7 @@

-    // Test with a bad escape; \b is unsupported.
+    // Test with a bad escape; \z is unsupported.
     re_error_t error{};
-    res = re->substitute(subj, L"AAA\\bZZZ", sflags, 0, &error);
+    res = re->substitute(subj, L"AAA\\zZZZ", sflags, 0, &error);
     do_test(!res.has_value());
     do_test(error.code == -57 /* PCRE2_ERROR_BADREPESCAPE */);
     do_test(error.message() == L"bad escape sequence in replacement string");