diff --git a/britney2/__init__.py b/britney2/__init__.py
index 6fc274b..f5deae2 100644
--- a/britney2/__init__.py
+++ b/britney2/__init__.py
@@ -85,6 +85,14 @@ class Suite(object):
         """
         return pkg_id in self._all_binaries_in_suite
 
+    def which_of_these_are_in_the_suite(self, pkgs):
+        """Iterate over all packages that are in the suite
+
+        :param pkgs: An iterable of package ids
+        :return: An iterable of package ids that are in the suite
+        """
+        yield from (x for x in pkgs if x in self._all_binaries_in_suite)
+
 
 class TargetSuite(Suite):
 
@@ -110,6 +118,14 @@ class TargetSuite(Suite):
         """
         return self.inst_tester.is_pkg_in_the_suite(pkg_id)
 
+    def which_of_these_are_in_the_suite(self, pkgs):
+        """Iterate over all packages that are in the suite
+
+        :param pkgs: An iterable of package ids
+        :return: An iterable of package ids that are in the suite
+        """
+        yield from self.inst_tester.which_of_these_are_in_the_suite(pkgs)
+
     def is_installable(self, pkg_id):
         """Determine whether the given package can be installed in the suite
 
diff --git a/britney2/installability/tester.py b/britney2/installability/tester.py
index 2f5d3d4..5ac6ef2 100644
--- a/britney2/installability/tester.py
+++ b/britney2/installability/tester.py
@@ -106,6 +106,14 @@ class InstallabilityTester(object):
         """
         return pkg_id in self._suite_contents
 
+    def which_of_these_are_in_the_suite(self, pkgs):
+        """Iterate over all packages that are in the suite
+
+        :param pkgs: An iterable of package ids
+        :return: An iterable of package ids that are in the suite
+        """
+        yield from (x for x in pkgs if x in self._suite_contents)
+
     def add_binary(self, pkg_id):
         """Add a binary package to the suite
 
diff --git a/britney2/policies/autopkgtest.py b/britney2/policies/autopkgtest.py
index 86c236a..4cd9854 100644
--- a/britney2/policies/autopkgtest.py
+++ b/britney2/policies/autopkgtest.py
@@ -73,6 +73,15 @@ def srchash(src):
         return src[0]
 
 
+def added_pkgs_compared_to_target_suite(package_ids, target_suite, *, invert=False):
+    if invert:
+        pkgs_ids_to_ignore = package_ids - set(target_suite.which_of_these_are_in_the_suite(package_ids))
+        names_ignored = {p.package_name for p in pkgs_ids_to_ignore}
+    else:
+        names_ignored = {p.package_name for p in target_suite.which_of_these_are_in_the_suite(package_ids)}
+    yield from (p for p in package_ids if p.package_name not in names_ignored)
+
+
 class AutopkgtestPolicy(BasePolicy):
     """autopkgtest regression policy for source migrations
 
@@ -514,19 +523,10 @@ class AutopkgtestPolicy(BasePolicy):
             # will also show up, but they are already properly
             # installed. Nevermind.
             depends = pkg_universe.dependencies_of(binary)
-            names_testing = set()
-            names_unstable = set()
             # depends is a frozenset{frozenset{BinaryPackageId, ..}}
             for deps_of_bin in depends:
-                for dep in deps_of_bin:
-                    if target_suite.is_pkg_in_the_suite(dep):
-                        names_testing.add(dep.package_name)
-                    else:
-                        names_unstable.add(dep.package_name)
-            for name in names_unstable - names_testing:
-                for deps_of_bin in depends:
-                    # We'll figure out which version later
-                    bin_new.update(d for d in deps_of_bin if d.package_name == name)
+                # We'll figure out which version later
+                bin_new.update(added_pkgs_compared_to_target_suite(deps_of_bin, target_suite))
 
         # Check if the package breaks/conflicts anything. We might
         # be adding slightly too many source packages due to the
@@ -537,16 +537,8 @@ class AutopkgtestPolicy(BasePolicy):
         for binary in bin_triggers:
             # broken is a frozenset{BinaryPackageId, ..}
             broken = pkg_universe.negative_dependencies_of(binary)
-            names_testing = set()
-            names_unstable = set()
-            for broken_bin in broken:
-                if target_suite.is_pkg_in_the_suite(broken_bin):
-                    names_testing.add(broken_bin.package_name)
-                else:
-                    names_unstable.add(broken_bin.package_name)
-            for name in names_testing - names_unstable:
-                # We'll figure out which version later
-                bin_broken.update(b for b in broken if b.package_name == name)
+            # We'll figure out which version later
+            bin_broken.update(added_pkgs_compared_to_target_suite(broken, target_suite, invert=True))
         bin_triggers.update(bin_broken)
 
         triggers = set()