diff --git a/alibuild_helpers/utilities.py b/alibuild_helpers/utilities.py
index 45abd99e..33973001 100644
--- a/alibuild_helpers/utilities.py
+++ b/alibuild_helpers/utilities.py
@@ -21,7 +21,7 @@
 
 from alibuild_helpers.cmd import decode_with_fallback, getoutput
 from alibuild_helpers.git import git
-from alibuild_helpers.log import dieOnError
+from alibuild_helpers.log import warning, dieOnError
 
 
 class SpecError(Exception):
@@ -383,10 +383,18 @@ def getPackageList(packages, specs, configDir, preferSystem, noSystem,
     dieOnError(spec["package"].lower() != pkg_filename,
                "%s.sh has different package field: %s" % (p, spec["package"]))
 
-    # Re-rewrite the defaults' name to "defaults-release". Everything auto-
-    # depends on "defaults-release", so we need something with that name.
     if p == "defaults-release":
+      # Re-rewrite the defaults' name to "defaults-release". Everything auto-
+      # depends on "defaults-release", so we need something with that name.
       spec["package"] = "defaults-release"
+
+      # Never run the defaults' recipe, to match previous behaviour.
+      # Warn if a non-trivial recipe is found (i.e., one with any non-comment lines).
+      for line in map(str.strip, recipe.splitlines()):
+        if line and not line.startswith("#"):
+          warning("%s.sh contains a recipe, which will be ignored", pkg_filename)
+      recipe = ""
+
     dieOnError(spec["package"] != p,
                "%s should be spelt %s." % (p, spec["package"]))
 
diff --git a/tests/test_build.py b/tests/test_build.py
index da46f0d0..2b0fef4d 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -26,6 +26,7 @@
 package: defaults-release
 version: v1
 ---
+: this line should trigger a warning
 """
 TEST_DEFAULT_RELEASE_BUILD_HASH = "27ce49698e818e8efb56b6eff6dd785e503df341"
 
@@ -206,6 +207,7 @@ class BuildTestCase(unittest.TestCase):
     @patch("alibuild_helpers.build.sys")
     @patch("alibuild_helpers.build.dieOnError", new=MagicMock())
     @patch("alibuild_helpers.utilities.dieOnError", new=MagicMock())
+    @patch("alibuild_helpers.utilities.warning")
     @patch("alibuild_helpers.build.readDefaults",
            new=MagicMock(return_value=(OrderedDict({"package": "defaults-release", "disable": []}), "")))
     @patch("alibuild_helpers.build.makedirs", new=MagicMock(return_value=None))
@@ -225,9 +227,10 @@ class BuildTestCase(unittest.TestCase):
     @patch("alibuild_helpers.workarea.is_writeable", new=MagicMock(return_value=True))
     @patch("alibuild_helpers.build.basename", new=MagicMock(return_value="aliBuild"))
     @patch("alibuild_helpers.build.install_wrapper_script", new=MagicMock())
-    def test_coverDoBuild(self, mock_debug, mock_glob, mock_sys, mock_git_git):
+    def test_coverDoBuild(self, mock_debug, mock_glob, mock_warning, mock_sys, mock_git_git):
         mock_git_git.side_effect = dummy_git
         mock_debug.side_effect = lambda *args: None
+        mock_warning.side_effect = lambda *args: None
         mock_glob.side_effect = lambda x: {
             "*": ["zlib"],
             "/sw/TARS/osx_x86-64/defaults-release/defaults-release-v1-*.osx_x86-64.tar.gz": ["/sw/TARS/osx_x86-64/defaults-release/defaults-release-v1-1.osx_x86-64.tar.gz"],
@@ -286,8 +289,10 @@ def test_coverDoBuild(self, mock_debug, mock_glob, mock_sys, mock_git_git):
 
         mock_git_git.reset_mock()
         mock_debug.reset_mock()
+        mock_warning.reset_mock()
         exit_code = doBuild(args, mock_parser)
         self.assertEqual(exit_code, 0)
+        mock_warning.assert_called_with("%s.sh contains a recipe, which will be ignored", "defaults-release")
         mock_debug.assert_called_with("Everything done")
         self.assertEqual(mock_git_git.call_count, len(common_calls))
         mock_git_git.assert_has_calls(common_calls, any_order=True)
@@ -295,9 +300,11 @@ def test_coverDoBuild(self, mock_debug, mock_glob, mock_sys, mock_git_git):
         # Force fetching repos
         mock_git_git.reset_mock()
         mock_debug.reset_mock()
+        mock_warning.reset_mock()
         args.fetchRepos = True
         exit_code = doBuild(args, mock_parser)
         self.assertEqual(exit_code, 0)
+        mock_warning.assert_called_with("%s.sh contains a recipe, which will be ignored", "defaults-release")
         mock_debug.assert_called_with("Everything done")
         mock_glob.assert_called_with("/sw/TARS/osx_x86-64/ROOT/ROOT-v6-08-30-*.osx_x86-64.tar.gz")
         # We can't compare directly against the list of calls here as they
@@ -311,7 +318,7 @@ def setup_spec(self, script):
         """Parse the alidist recipe in SCRIPT and return its spec."""
         err, spec, recipe = parseRecipe(lambda: script)
         self.assertIsNone(err)
-        spec["recipe"] = recipe.strip("\n")
+        spec["recipe"] = "" if spec["package"].startswith("defaults-") else recipe.strip("\n")
         spec.setdefault("tag", spec["version"])
         spec["tag"] = resolve_tag(spec)
         return spec