diff --git a/plinth/package.py b/plinth/package.py
index e189e84a1..ca7c56407 100644
--- a/plinth/package.py
+++ b/plinth/package.py
@@ -268,11 +268,23 @@ class Packages(app_module.FollowerComponent):
         except MissingPackageError:
             pass  # We will retry after refreshing package list
 
-        # If the package cache is new, then package is really not available.
         package_cache = pathlib.Path('/var/cache/apt/pkgcache.bin')
-        if (package_cache.exists()
-                and time.time() - package_cache.stat().st_mtime < 3600):
-            return False
+        if package_cache.exists():
+            package_cache_mtime = package_cache.stat().st_mtime
+
+            sources_dir = pathlib.Path('/etc/apt/sources.list.d')
+            source_files = ([pathlib.Path('/etc/apt/sources.list')] +
+                            list(sources_dir.glob('*.list')) +
+                            list(sources_dir.glob('*.sources')))
+            are_sources_newer = any(
+                source_file.stat().st_mtime > package_cache_mtime
+                for source_file in source_files)
+
+            # If the package cache is new, then package is really not
+            # available.
+            if (time.time() - package_cache.stat().st_mtime < 3600
+                    and not are_sources_newer):
+                return False
 
         # Perform 'apt-get update'
         refresh_package_lists()
diff --git a/plinth/tests/test_package.py b/plinth/tests/test_package.py
index 137418a97..b7aea85c3 100644
--- a/plinth/tests/test_package.py
+++ b/plinth/tests/test_package.py
@@ -344,8 +344,19 @@ def test_packages_find_conflicts(packages_installed_):
 @patch('pathlib.Path')
 def test_packages_is_available(path_class, cache, refresh_package_lists):
     """Test checking for available packages."""
-    path = Mock()
-    path_class.return_value = path
+    package_cache = Mock()
+    sources_dir = Mock()
+    sources_dir.glob.return_value = []
+    sources_list = Mock()
+
+    def path_side_effect(path):
+        return {
+            '/var/cache/apt/pkgcache.bin': package_cache,
+            '/etc/apt/sources.list.d': sources_dir,
+            '/etc/apt/sources.list': sources_list
+        }[path]
+
+    path_class.side_effect = path_side_effect
 
     # Packages found in cache
     component = Packages('test-component', ['package1', 'package2'])
@@ -356,22 +367,32 @@ def test_packages_is_available(path_class, cache, refresh_package_lists):
 
     # Packages not found, cache exists and is fresh
     cache.return_value = ['package1']
-    path.exists.return_value = True
-    path.stat.return_value.st_mtime = time.time()
+    package_cache.exists.return_value = True
+    package_cache.stat.return_value.st_mtime = time.time()
+    sources_list.stat.return_value.st_mtime = time.time() - 100
     assert not component.is_available()
     refresh_package_lists.assert_not_called()
 
     # Packages not found, cache does not exist
     cache.return_value = ['package1']
-    path.exists.return_value = False
+    package_cache.exists.return_value = False
     assert not component.is_available()
     refresh_package_lists.assert_called_once()
 
-    # Packages not found, cache is stale
+    # Packages not found, cache is stale because it older than 1 hour
     cache.return_value = ['package1']
     refresh_package_lists.reset_mock()
-    path.exists.return_value = True
-    path.stat.return_value.st_mtime = time.time() - 7200
+    package_cache.exists.return_value = True
+    package_cache.stat.return_value.st_mtime = time.time() - 7200
+    assert not component.is_available()
+    refresh_package_lists.assert_called_once()
+
+    # Packages not found, cache is stale because it older than sources.list
+    cache.return_value = ['package1']
+    refresh_package_lists.reset_mock()
+    package_cache.exists.return_value = True
+    package_cache.stat.return_value.st_mtime = time.time() - 100
+    sources_list.stat.return_value.st_mtime = time.time()
     assert not component.is_available()
     refresh_package_lists.assert_called_once()