diff --git a/doc_src/language.rst b/doc_src/language.rst
index 824cad052..159fa30f9 100644
--- a/doc_src/language.rst
+++ b/doc_src/language.rst
@@ -1586,7 +1586,7 @@ You can see the current list of features via ``status features``::
 
 Here is what they mean:
 
-- ``stderr-nocaret`` was introduced in fish 3.0 (and made the default in 3.3). It makes ``^`` an ordinary character instead of denoting an stderr redirection, to make dealing with quoting and such easier. Use ``2>`` instead.
+- ``stderr-nocaret`` was introduced in fish 3.0 (and made the default in 3.3). It makes ``^`` an ordinary character instead of denoting an stderr redirection, to make dealing with quoting and such easier. Use ``2>`` instead. This can no longer be turned off since fish 3.5. The flag can still be tested for compatibility, but a ``no-stderr-nocaret`` value will simply be ignored.
 - ``qmark-noglob`` was also introduced in fish 3.0. It makes ``?`` an ordinary character instead of a single-character glob. Use a ``*`` instead (which will match multiple characters) or find other ways to match files like ``find``.
 - ``regex-easyesc`` was introduced in 3.1. It makes it so the replacement expression in ``string replace -r`` does one fewer round of escaping. Before, to escape a backslash you would have to use ``string replace -ra '([ab])' '\\\\\\\\$1'``. After, just ``'\\\\$1'`` is enough. Check your ``string replace`` cals if you use this anywhere.
 - ``ampersand-nobg-in-token`` was introduced in fish 3.4. It makes it so a ``&`` i no longer interpreted as the backgrounding operator in the middle of a token, so dealing with URLs becomes easier. Either put spaces or a semicolon after the ``&``. This is recommended formatting anyway, and ``fish_indent`` will have done it for you already.
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 0f6253624..688205132 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -1937,16 +1937,10 @@ static void test_feature_flags() {
     say(L"Testing future feature flags");
     using ft = features_t;
     ft f;
-    do_test(f.test(ft::stderr_nocaret));
-    f.set(ft::stderr_nocaret, true);
-    do_test(f.test(ft::stderr_nocaret));
-    f.set(ft::stderr_nocaret, false);
-    do_test(!f.test(ft::stderr_nocaret));
-
     f.set_from_string(L"stderr-nocaret,nonsense");
     do_test(f.test(ft::stderr_nocaret));
     f.set_from_string(L"stderr-nocaret,no-stderr-nocaret,nonsense");
-    do_test(!f.test(ft::stderr_nocaret));
+    do_test(f.test(ft::stderr_nocaret));
 
     // Ensure every metadata is represented once.
     size_t counts[ft::flag_count] = {};
diff --git a/src/future_feature_flags.cpp b/src/future_feature_flags.cpp
index df287b9af..d33fa8b63 100644
--- a/src/future_feature_flags.cpp
+++ b/src/future_feature_flags.cpp
@@ -16,12 +16,12 @@ features_t::features_t() {
 features_t features_t::global_features;
 
 const features_t::metadata_t features_t::metadata[features_t::flag_count] = {
-    {stderr_nocaret, L"stderr-nocaret", L"3.0", L"^ no longer redirects stderr", true},
-    {qmark_noglob, L"qmark-noglob", L"3.0", L"? no longer globs", false},
+    {stderr_nocaret, L"stderr-nocaret", L"3.0", L"^ no longer redirects stderr", true, true /* read-only */},
+    {qmark_noglob, L"qmark-noglob", L"3.0", L"? no longer globs", false, false},
     {string_replace_backslash, L"regex-easyesc", L"3.1", L"string replace -r needs fewer \\'s",
-     true},
+     true, false},
     {ampersand_nobg_in_token, L"ampersand-nobg-in-token", L"3.4",
-     L"& only backgrounds if followed by a separator", false},
+     L"& only backgrounds if followed by a separator", false, false},
 };
 
 const struct features_t::metadata_t *features_t::metadata_for(const wchar_t *name) {
@@ -55,11 +55,17 @@ void features_t::set_from_string(const wcstring &str) {
         // future versions).
         // The special name 'all' may be used for those who like to live on the edge.
         if (const metadata_t *md = metadata_for(name)) {
-            this->set(md->flag, value);
+            // Only change it if it's not read-only.
+            // Don't complain if it is, this is typically set from a variable.
+            if (!md->read_only) {
+                this->set(md->flag, value);
+            }
         } else {
             for (const metadata_t &md : metadata) {
                 if (std::wcsstr(md.groups, name) || !std::wcscmp(name, L"all")) {
-                    this->set(md.flag, value);
+                    if (!md.read_only) {
+                        this->set(md.flag, value);
+                    }
                 }
             }
         }
diff --git a/src/future_feature_flags.h b/src/future_feature_flags.h
index 9ddb5efc4..12fd897cb 100644
--- a/src/future_feature_flags.h
+++ b/src/future_feature_flags.h
@@ -63,6 +63,9 @@ class features_t {
 
         /// Default flag value.
         const bool default_value;
+
+        /// Whether the value can still be changed or not.
+        const bool read_only;
     };
 
     /// The metadata, indexed by flag.
diff --git a/tests/checks/features-nocaret1.fish b/tests/checks/features-nocaret1.fish
index a7230e594..c0b18c671 100644
--- a/tests/checks/features-nocaret1.fish
+++ b/tests/checks/features-nocaret1.fish
@@ -1,2 +1,2 @@
 #RUN: %fish --features 'no-stderr-nocaret' -c 'status test-feature stderr-nocaret; echo nocaret: $status'
-# CHECK: nocaret: 1
+# CHECK: nocaret: 0
diff --git a/tests/checks/features-nocaret3.fish b/tests/checks/features-nocaret3.fish
index 4f353d2b6..ed4575452 100644
--- a/tests/checks/features-nocaret3.fish
+++ b/tests/checks/features-nocaret3.fish
@@ -1,2 +1,2 @@
 #RUN: %fish --features 'no-stderr-nocaret' -c 'echo -n careton:; echo ^/dev/null'
-# CHECK: careton:
+# CHECK: careton:^/dev/null
diff --git a/tests/checks/features-nocaret5.fish b/tests/checks/features-nocaret5.fish
deleted file mode 100644
index 67db8e58a..000000000
--- a/tests/checks/features-nocaret5.fish
+++ /dev/null
@@ -1,2 +0,0 @@
-#RUN: %fish --features no-stderr-nocaret -c 'cat /abavojijsdfhdsjhfuihifoisj ^&1'
-# CHECK: {{cat|/abavojijsdfhdsjhfuihifoisj}}: {{.*}}