diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index fd8b4b287..b4c792480 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -1251,24 +1251,25 @@ BULITIN_DIR_NOPREFIX_OPTIONS: T.Dict[OptionKey, T.Dict[str, str]] = {
     OptionKey('purelibdir', module='python'): {},
 }
 
-FORBIDDEN_TARGET_NAMES = {'clean': None,
-                          'clean-ctlist': None,
-                          'clean-gcno': None,
-                          'clean-gcda': None,
-                          'coverage': None,
-                          'coverage-text': None,
-                          'coverage-xml': None,
-                          'coverage-html': None,
-                          'phony': None,
-                          'PHONY': None,
-                          'all': None,
-                          'test': None,
-                          'benchmark': None,
-                          'install': None,
-                          'uninstall': None,
-                          'build.ninja': None,
-                          'scan-build': None,
-                          'reconfigure': None,
-                          'dist': None,
-                          'distcheck': None,
-                          }
+FORBIDDEN_TARGET_NAMES = frozenset({
+    'clean',
+    'clean-ctlist',
+    'clean-gcno',
+    'clean-gcda',
+    'coverage',
+    'coverage-text',
+    'coverage-xml',
+    'coverage-html',
+    'phony',
+    'PHONY',
+    'all',
+    'test',
+    'benchmark',
+    'install',
+    'uninstall',
+    'build.ninja',
+    'scan-build',
+    'reconfigure',
+    'dist',
+    'distcheck',
+})
diff --git a/unittests/allplatformstests.py b/unittests/allplatformstests.py
index a98cd9414..ac60907a5 100644
--- a/unittests/allplatformstests.py
+++ b/unittests/allplatformstests.py
@@ -1507,12 +1507,12 @@ class AllPlatformTests(BasePlatformTests):
         test. Needs to be a unit test because it accesses Meson internals.
         '''
         testdir = os.path.join(self.common_test_dir, '150 reserved targets')
-        targets = mesonbuild.coredata.FORBIDDEN_TARGET_NAMES
+        targets = set(mesonbuild.coredata.FORBIDDEN_TARGET_NAMES)
         # We don't actually define a target with this name
-        targets.pop('build.ninja')
+        targets.remove('build.ninja')
         # Remove this to avoid multiple entries with the same name
         # but different case.
-        targets.pop('PHONY')
+        targets.remove('PHONY')
         for i in targets:
             self.assertPathExists(os.path.join(testdir, i))