diff --git a/fdroidserver/metadata.py b/fdroidserver/metadata.py
index 4b62878e..869253c7 100644
--- a/fdroidserver/metadata.py
+++ b/fdroidserver/metadata.py
@@ -1049,6 +1049,7 @@ def _format_stringmap(appid, field, stringmap, versionCode=None):
     try:
         next(app_dir.glob('*/%s/*.txt' % field.lower()))
         files = []
+        overwrites = []
         for name, descdict in stringmap.items():
             for locale, desc in descdict.items():
                 outdir = app_dir / locale / field.lower()
@@ -1058,8 +1059,21 @@ def _format_stringmap(appid, field, stringmap, versionCode=None):
                     filename = '%s.txt' % name
                 outfile = outdir / filename
                 files.append(str(outfile))
-                with outfile.open('w') as fp:
-                    fp.write(desc)
+                if outfile.exists():
+                    if desc != outfile.read_text():
+                        overwrites.append(str(outfile))
+                else:
+                    if not outfile.parent.exists():
+                        outfile.parent.mkdir(parents=True)
+                    outfile.write_text(desc)
+        if overwrites:
+            _warn_or_exception(
+                _(
+                    'Conflicting "{field}" definitions between .yml and localized files:'
+                ).format(field=field)
+                + '\n'
+                + '\n'.join(sorted(overwrites))
+            )
         logging.warning(
             _('Moving Anti-Features declarations to localized files:')
             + '\n'
diff --git a/tests/metadata.TestCase b/tests/metadata.TestCase
index fb17c6df..59c2bafe 100755
--- a/tests/metadata.TestCase
+++ b/tests/metadata.TestCase
@@ -1858,6 +1858,55 @@ class MetadataTest(unittest.TestCase):
             {'AF': {'ko': 'b', 'uz': 'a', 'zh': 'c'}},
         )
 
+    def test_format_stringmap_app_antifeatures_conflict(self):
+        """Raise an error if a YAML Anti-Feature conflicts with a localized file."""
+        os.chdir(self.testdir)
+        appid = 'a'
+        field = 'AntiFeatures'
+        locale = 'ko'
+        yml = Path('metadata/a.yml')
+        antifeatures_ko = yml.parent / appid / locale / field.lower()
+        antifeatures_ko.mkdir(parents=True)
+        afname = 'Anti-🔥'
+        (antifeatures_ko / (afname + '.txt')).write_text('SOMETHING ELSE')
+        with self.assertRaises(MetaDataException):
+            metadata._format_stringmap(
+                appid, field, {afname: {'uz': 'a', locale: 'b', 'zh': 'c'}}
+            )
+
+    def test_format_stringmap_app_antifeatures_conflict_same_contents(self):
+        """Raise an error if a YAML Anti-Feature conflicts with a localized file."""
+        os.chdir(self.testdir)
+        appid = 'a'
+        field = 'AntiFeatures'
+        locale = 'ko'
+        yml = Path('metadata/a.yml')
+        antifeatures_ko = yml.parent / appid / locale / field.lower()
+        antifeatures_ko.mkdir(parents=True)
+        afname = 'Anti-🔥'
+        (antifeatures_ko / (afname + '.txt')).write_text('b')
+        metadata._format_stringmap(
+            appid, field, {afname: {'uz': 'a', locale: 'b', 'zh': 'c'}}
+        )
+
+    def test_format_stringmap_build_antifeatures_conflict(self):
+        """Raise an error if a YAML Anti-Feature conflicts with a localized file."""
+        os.chdir(self.testdir)
+        appid = 'a'
+        field = 'antifeatures'
+        locale = 'ko'
+        versionCode = 123
+        yml = Path('metadata/a.yml')
+        antifeatures_ko = yml.parent / appid / locale / field.lower()
+        antifeatures_ko.mkdir(parents=True)
+        afname = 'Anti-🔥'
+        with (antifeatures_ko / ('%d_%s.txt' % (versionCode, afname))).open('w') as fp:
+            fp.write('SOMETHING ELSE')
+        with self.assertRaises(MetaDataException):
+            metadata._format_stringmap(
+                appid, field, {afname: {'uz': 'a', locale: 'b', 'zh': 'c'}}, versionCode
+            )
+
 
 class PostMetadataParseTest(unittest.TestCase):
     """Test the functions that post process the YAML input.