diff --git a/tests/base.py b/tests/base.py
index 0f8b3af6eb..2bcd1ca19a 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -1928,7 +1928,7 @@ class ZuulTestCase(BaseTestCase):
         self.sched.reconfigure(self.config)
         self.sched.resume()
 
-    def configure_connections(self):
+    def configure_connections(self, source_only=False):
         # Set up gerrit related fakes
         # Set a changes database so multiple FakeGerrit's can report back to
         # a virtual canonical database given by the configured hostname
@@ -1971,7 +1971,7 @@ class ZuulTestCase(BaseTestCase):
 
         # Register connections from the config using fakes
         self.connections = zuul.lib.connections.ConnectionRegistry()
-        self.connections.configure(self.config)
+        self.connections.configure(self.config, source_only=source_only)
 
     def setup_config(self):
         # This creates the per-test configuration object.  It can be
diff --git a/tests/fixtures/zuul-connections-merger.conf b/tests/fixtures/zuul-connections-merger.conf
new file mode 100644
index 0000000000..7a1bc42b2a
--- /dev/null
+++ b/tests/fixtures/zuul-connections-merger.conf
@@ -0,0 +1,35 @@
+[gearman]
+server=127.0.0.1
+
+[zuul]
+job_name_in_report=true
+status_url=http://zuul.example.com/status
+
+[merger]
+git_dir=/tmp/zuul-test/git
+git_user_email=zuul@example.com
+git_user_name=zuul
+zuul_url=http://zuul.example.com/p
+
+[executor]
+git_dir=/tmp/zuul-test/executor-git
+
+[connection github]
+driver=github
+
+[connection gerrit]
+driver=gerrit
+server=review.example.com
+user=jenkins
+sshkey=fake_id_rsa1
+
+[connection resultsdb]
+driver=sql
+dburi=$MYSQL_FIXTURE_DBURI$
+
+[connection smtp]
+driver=smtp
+server=localhost
+port=25
+default_from=zuul@example.com
+default_to=you@example.com
diff --git a/tests/unit/test_connection.py b/tests/unit/test_connection.py
index db32938281..92270b7320 100644
--- a/tests/unit/test_connection.py
+++ b/tests/unit/test_connection.py
@@ -265,3 +265,21 @@ class TestMultipleGerrits(ZuulTestCase):
         self.executor_server.hold_jobs_in_build = False
         self.executor_server.release()
         self.waitUntilSettled()
+
+
+class TestConnectionsMerger(ZuulTestCase):
+    config_file = 'zuul-connections-merger.conf'
+    tenant_config_file = 'config/single-tenant/main.yaml'
+
+    def configure_connections(self):
+        super(TestConnectionsMerger, self).configure_connections(True)
+
+    def test_connections_merger(self):
+        "Test merger only configures source connections"
+
+        self.assertIn("gerrit", self.connections.connections)
+        self.assertIn("github", self.connections.connections)
+        self.assertNotIn("smtp", self.connections.connections)
+        self.assertNotIn("sql", self.connections.connections)
+        self.assertNotIn("timer", self.connections.connections)
+        self.assertNotIn("zuul", self.connections.connections)
diff --git a/zuul/lib/connections.py b/zuul/lib/connections.py
index 720299a0ca..9908fff9e8 100644
--- a/zuul/lib/connections.py
+++ b/zuul/lib/connections.py
@@ -105,7 +105,7 @@ class ConnectionRegistry(object):
             # The merger and the reporter only needs source driver.
             # This makes sure Reporter like the SQLDriver are only created by
             # the scheduler process
-            if source_only and not issubclass(driver, SourceInterface):
+            if source_only and not isinstance(driver, SourceInterface):
                 continue
 
             connection = driver.getConnection(con_name, con_config)
@@ -138,10 +138,11 @@ class ConnectionRegistry(object):
 
         # Create default connections for drivers which need no
         # connection information (e.g., 'timer' or 'zuul').
-        for driver in self.drivers.values():
-            if not hasattr(driver, 'getConnection'):
-                connections[driver.name] = DefaultConnection(
-                    driver, driver.name, {})
+        if not source_only:
+            for driver in self.drivers.values():
+                if not hasattr(driver, 'getConnection'):
+                    connections[driver.name] = DefaultConnection(
+                        driver, driver.name, {})
 
         self.connections = connections