diff --git a/fdroidserver/common.py b/fdroidserver/common.py
index 55cb2b65..acccf63a 100644
--- a/fdroidserver/common.py
+++ b/fdroidserver/common.py
@@ -1518,7 +1518,19 @@ def parse_androidmanifests(paths, app):
 
 
 def is_valid_package_name(name):
-    return re.match("[A-Za-z_][A-Za-z_0-9.]+$", name)
+    """Check whether name is a valid fdroid package name
+
+    APKs and manually defined package names must use a valid Java
+    Package Name.  Automatically generated package names for non-APK
+    files use the SHA-256 sum.
+
+    """
+    return re.match("^([a-f0-9]+|[A-Za-z_][A-Za-z_0-9.]+)$", name)
+
+
+def is_valid_java_package_name(name):
+    """Check whether name is a valid Java package name aka Application ID"""
+    return re.match("^[A-Za-z_][A-Za-z_0-9.]+$", name)
 
 
 def getsrclib(spec, srclib_dir, subdir=None, basepath=False,
diff --git a/fdroidserver/metadata.py b/fdroidserver/metadata.py
index 02e7bc3d..273ecb80 100644
--- a/fdroidserver/metadata.py
+++ b/fdroidserver/metadata.py
@@ -805,6 +805,9 @@ def read_metadata(xref=True, check_vcs=[], refresh=True, sort_by_time=False):
         if metadatapath == '.fdroid.txt':
             warn_or_exception(_('.fdroid.txt is not supported!  Convert to .fdroid.yml or .fdroid.json.'))
         appid, _ignored = fdroidserver.common.get_extension(os.path.basename(metadatapath))
+        if appid != '.fdroid' and not fdroidserver.common.is_valid_package_name(appid):
+            warn_or_exception(_("{appid} from {path} is not a valid Java Package Name!")
+                              .format(appid=appid, path=metadatapath))
         if appid in apps:
             warn_or_exception(_("Found multiple metadata files for {appid}")
                               .format(appid=appid))
diff --git a/tests/common.TestCase b/tests/common.TestCase
index 1c75a411..ef614a56 100755
--- a/tests/common.TestCase
+++ b/tests/common.TestCase
@@ -158,9 +158,10 @@ class CommonTest(unittest.TestCase):
             self.assertFalse(debuggable,
                              "debuggable APK state was not properly parsed!")
 
-    def testPackageNameValidity(self):
+    def test_is_valid_package_name(self):
         for name in ["org.fdroid.fdroid",
-                     "org.f_droid.fdr0ID"]:
+                     "org.f_droid.fdr0ID",
+                     "05041684efd9b16c2888b1eddbadd0359f655f311b89bdd1737f560a10d20fb8"]:
             self.assertTrue(fdroidserver.common.is_valid_package_name(name),
                             "{0} should be a valid package name".format(name))
         for name in ["0rg.fdroid.fdroid",
@@ -170,6 +171,19 @@ class CommonTest(unittest.TestCase):
             self.assertFalse(fdroidserver.common.is_valid_package_name(name),
                              "{0} should not be a valid package name".format(name))
 
+    def test_is_valid_java_package_name(self):
+        for name in ["org.fdroid.fdroid",
+                     "org.f_droid.fdr0ID"]:
+            self.assertTrue(fdroidserver.common.is_valid_java_package_name(name),
+                            "{0} should be a valid package name".format(name))
+        for name in ["0rg.fdroid.fdroid",
+                     ".f_droid.fdr0ID",
+                     "org.fdroid/fdroid",
+                     "/org.fdroid.fdroid",
+                     "05041684efd9b16c2888b1eddbadd0359f655f311b89bdd1737f560a10d20fb8"]:
+            self.assertFalse(fdroidserver.common.is_valid_java_package_name(name),
+                             "{0} should not be a valid package name".format(name))
+
     def test_prepare_sources(self):
         testint = 99999999
         teststr = 'FAKE_STR_FOR_TESTING'