diff --git a/aliBuild b/aliBuild
index dc1c56f2..16ab091d 100755
--- a/aliBuild
+++ b/aliBuild
@@ -57,7 +57,7 @@ def doMain(args, parser):
       error(e.message)
       exit(1)
 
-  if args.action == "version":
+  if args.action == "version" or args.action == None:
     print("aliBuild version: {version} ({arch})".format(
       version=__version__ or "unknown", arch=args.architecture or "unknown"))
     sys.exit(0)
diff --git a/alibuild_helpers/build.py b/alibuild_helpers/build.py
index c6817a78..72ec011c 100644
--- a/alibuild_helpers/build.py
+++ b/alibuild_helpers/build.py
@@ -4,8 +4,8 @@
 from alibuild_helpers.analytics import report_event
 from alibuild_helpers.log import debug, info, banner, warning
 from alibuild_helpers.log import dieOnError
-from alibuild_helpers.cmd import execute, DockerRunner, BASH, install_wrapper_script
-from alibuild_helpers.utilities import prunePaths, symlink, call_ignoring_oserrors, topological_sort
+from alibuild_helpers.cmd import execute, DockerRunner, BASH, install_wrapper_script, getstatusoutput
+from alibuild_helpers.utilities import prunePaths, symlink, call_ignoring_oserrors, topological_sort, detectArch
 from alibuild_helpers.utilities import resolve_store_path
 from alibuild_helpers.utilities import parseDefaults, readDefaults
 from alibuild_helpers.utilities import getPackageList, asList
@@ -1112,6 +1112,29 @@ def doBuild(args, parser):
       """)
       buildErrMsg += "".join("\n  ( cd %s && git pull --rebase )" % dp for dp in updatablePkgs)
 
+    # Gather build info for the error message
+    try:
+      safe_args = {
+        "pkgname", "defaults", "architecture", "forceUnknownArch",
+        "develPrefix", "jobs", "noSystem", "noDevel", "forceTracked", "plugin",
+        "disable", "annotate", "onlyDeps", "docker"
+          }
+      args_str = " ".join(f"--{k}={v}" for k, v in vars(args).items() if v and k in safe_args)
+      detected_arch = detectArch()
+      buildErrMsg += dedent(f"""
+      Build info:
+      OS: {detected_arch}
+      Using aliBuild from alibuild@{__version__ or "unknown"} recipes in alidist@{os.environ["ALIBUILD_ALIDIST_HASH"][:10]}
+      Build arguments: {args_str}
+      """)
+
+      if detected_arch.startswith("osx"):
+        buildErrMsg += f'XCode version: {getstatusoutput("xcodebuild -version")[1]}'
+
+    except Exception as exc:
+      warning("Failed to gather build info", exc_info=exc)
+
+
     dieOnError(err, buildErrMsg.strip())
 
     # We need to create 2 sets of links, once with the full requires,
diff --git a/alibuild_helpers/utilities.py b/alibuild_helpers/utilities.py
index ef90d2df..88ca6077 100644
--- a/alibuild_helpers/utilities.py
+++ b/alibuild_helpers/utilities.py
@@ -493,27 +493,28 @@ def getPackageList(packages, specs, configDir, preferSystem, noSystem,
             if re.match(replacement_matcher, key):
               replacement = spec["prefer_system_replacement_specs"][replacement_matcher]
               break
-          dieOnError(replacement is None, "Could not find named replacement spec for "
-                     "%s: %s" % (spec["package"], key))
-          assert(replacement)
-          # We must keep the package name the same, since it is used to
-          # specify dependencies.
-          replacement["package"] = spec["package"]
-          # The version is required for all specs. What we put there will
-          # influence the package's hash, so allow the user to override it.
-          replacement.setdefault("version", requested_version)
-          spec = replacement
-          # Allows generalising the version based on the actual key provided
-          spec["version"] = spec["version"].replace("%(key)s", key)
-          recipe = replacement.get("recipe", "")
-          # If there's an explicitly-specified recipe, we're still building
-          # the package. If not, aliBuild will still "build" it, but it's
-          # basically instantaneous, so report to the user that we're taking
-          # it from the system.
-          if recipe:
-            ownPackages.add(spec["package"])
+          if replacement:
+            # We must keep the package name the same, since it is used to
+            # specify dependencies.
+            replacement["package"] = spec["package"]
+            # The version is required for all specs. What we put there will
+            # influence the package's hash, so allow the user to override it.
+            replacement.setdefault("version", requested_version)
+            spec = replacement
+            # Allows generalising the version based on the actual key provided
+            spec["version"] = spec["version"].replace("%(key)s", key)
+            recipe = replacement.get("recipe", "")
+            # If there's an explicitly-specified recipe, we're still building
+            # the package. If not, aliBuild will still "build" it, but it's
+            # basically instantaneous, so report to the user that we're taking
+            # it from the system.
+            if recipe:
+              ownPackages.add(spec["package"])
+            else:
+              systemPackages.add(spec["package"])
           else:
-            systemPackages.add(spec["package"])
+            warning(f"Could not find named replacement spec for {spec['package']}: {key}, "
+                    "falling back to building the package ourselves.")
 
     dieOnError(("system_requirement" in spec) and recipe.strip("\n\t "),
                "System requirements %s cannot have a recipe" % spec["package"])
diff --git a/tests/test_packagelist.py b/tests/test_packagelist.py
index e3601c0e..4813446c 100644
--- a/tests/test_packagelist.py
+++ b/tests/test_packagelist.py
@@ -154,17 +154,20 @@ def test_replacement_recipe_given(self) -> None:
         self.assertNotIn("with-replacement-recipe", systemPkgs)
         self.assertIn("with-replacement-recipe", ownPkgs)
 
-    @mock.patch("alibuild_helpers.utilities.dieOnError")
-    def test_missing_replacement_spec(self, mock_dieOnError) -> None:
-        """Check an error is thrown when the replacement spec is not found."""
-        assert_msg = "Could not find named replacement spec for missing-spec: missing_tag"
-        # Change the behaviour from sys.exit to a regular exception. Without it
-        # we don't stop execution properly and other asserts might trigger
-        mock_dieOnError.side_effect = lambda cond, _: (_ for _ in ()).throw(Exception("dieOnError called")) if cond else None
-        with self.assertRaises(Exception, msg=assert_msg) as context:
-            specs, systemPkgs, ownPkgs, failedReqs, validDefaults = \
-                getPackageListWithDefaults(["missing-spec"])
-        self.assertEqual(str(context.exception), "dieOnError called", msg=assert_msg)
+    @mock.patch("alibuild_helpers.utilities.warning")
+    def test_missing_replacement_spec(self, mock_warning):
+        """Check a warning is displayed when the replacement spec is not found."""
+        warning_msg = "falling back to building the package ourselves"
+        warning_exists = False
+        def side_effect(msg, *args, **kwargs):
+            nonlocal warning_exists
+            if warning_msg in str(msg):
+              warning_exists = True
+        mock_warning.side_effect = side_effect
+        specs, systemPkgs, ownPkgs, failedReqs, validDefaults = \
+            getPackageListWithDefaults(["missing-spec"])
+        self.assertTrue(warning_exists)
+
 
 
 @mock.patch("alibuild_helpers.utilities.getRecipeReader", new=MockReader)