diff --git a/docs/markdown/snippets/unknown-options-always-fatal.md b/docs/markdown/snippets/unknown-options-always-fatal.md
new file mode 100644
index 000000000000..ce982c3caebb
--- /dev/null
+++ b/docs/markdown/snippets/unknown-options-always-fatal.md
@@ -0,0 +1,5 @@
+## Unknown options are now always fatal
+
+Passing unknown options to "meson setup" or "meson configure" is now
+always fatal. That is, Meson will exit with an error code if this
+happens. Previous Meson versions only showed a warning message.
diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index c2604be3a82e..37d830de2f3b 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -758,7 +758,7 @@ def copy_build_options_from_regular_ones(self) -> None:
                 except KeyError:
                     continue
 
-    def set_options(self, options: T.Dict[OptionKey, T.Any], subproject: str = '', warn_unknown: bool = True) -> None:
+    def set_options(self, options: T.Dict[OptionKey, T.Any], subproject: str = '') -> None:
         if not self.is_cross_build():
             options = {k: v for k, v in options.items() if k.machine is not MachineChoice.BUILD}
         # Set prefix first because it's needed to sanitize other options
@@ -774,16 +774,15 @@ def set_options(self, options: T.Dict[OptionKey, T.Any], subproject: str = '', w
         for k, v in options.items():
             if k == pfk:
                 continue
-            elif k not in self.options:
-                unknown_options.append(k)
-            else:
+            elif k in self.options:
                 self.set_option(k, v)
-        if unknown_options and warn_unknown:
+            elif k.machine != MachineChoice.BUILD:
+                unknown_options.append(k)
+        if unknown_options:
             unknown_options_str = ', '.join(sorted(str(s) for s in unknown_options))
             sub = f'In subproject {subproject}: ' if subproject else ''
-            mlog.warning(f'{sub}Unknown options: "{unknown_options_str}"')
-            mlog.log('The value of new options can be set with:')
-            mlog.log(mlog.bold('meson setup <builddir> --reconfigure -Dnew_option=new_value ...'))
+            raise MesonException(f'{sub}Unknown options: "{unknown_options_str}"')
+
         if not self.is_cross_build():
             self.copy_build_options_from_regular_ones()
 
diff --git a/run_unittests.py b/run_unittests.py
index 324de94379e1..830678255f49 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -3306,8 +3306,6 @@ def test_lto_threads(self):
         if cc.get_id() == 'clang':
             if is_windows():
                 raise unittest.SkipTest('LTO not (yet) supported by windows clang')
-            else:
-                extra_args.append('-D_cargs=-Werror=unused-command-line-argument')
 
         self.init(testdir, extra_args=['-Db_lto=true', '-Db_lto_threads=8'] + extra_args)
         self.build()
@@ -4315,9 +4313,11 @@ def test_command_line(self):
             self.assertEqual(obj.options[OptionKey('default_library')].value, 'shared')
         self.wipe()
 
-        # Should warn on unknown options
-        out = self.init(testdir, extra_args=['-Dbad=1', '-Dfoo=2', '-Dwrong_link_args=foo'])
-        self.assertIn('Unknown options: "bad, foo, wrong_link_args"', out)
+        # Should fail on unknown options
+        with self.assertRaises((subprocess.CalledProcessError, RuntimeError)) as cm:
+            self.init(testdir, extra_args=['-Dbad=1', '-Dfoo=2', '-Dwrong_link_args=foo'])
+            self.assertNotEqual(0, cm.exception.returncode)
+            self.assertIn(msg, cm.exception.output)
         self.wipe()
 
         # Should fail on malformed option