diff --git a/securedrop/source_app/main.py b/securedrop/source_app/main.py
index d6c90f0fae..0921398597 100644
--- a/securedrop/source_app/main.py
+++ b/securedrop/source_app/main.py
@@ -2,6 +2,7 @@
 import os
 import io
 
+from base64 import urlsafe_b64encode
 from datetime import datetime
 from flask import (Blueprint, render_template, flash, redirect, url_for, g,
                    session, current_app, request, Markup, abort)
@@ -37,9 +38,17 @@ def generate():
             return redirect(url_for('.lookup'))
 
         codename = generate_unique_codename(config)
-        session['codename'] = codename
+
+        # Generate a unique id for each browser tab and associate the codename with this id.
+        # This will allow retrieval of the codename displayed in the tab from which the source has
+        # clicked to proceed to /generate (ref. issue #4458)
+        tab_id = urlsafe_b64encode(os.urandom(64)).decode()
+        codenames = session.get('codenames', {})
+        codenames[tab_id] = codename
+        session['codenames'] = codenames
+
         session['new_user'] = True
-        return render_template('generate.html', codename=codename)
+        return render_template('generate.html', codename=codename, tab_id=tab_id)
 
     @view.route('/org-logo')
     def select_logo():
@@ -51,33 +60,43 @@ def select_logo():
 
     @view.route('/create', methods=['POST'])
     def create():
-        filesystem_id = current_app.crypto_util.hash_codename(
-            session['codename'])
-
-        source = Source(filesystem_id, current_app.crypto_util.display_id())
-        db.session.add(source)
-        try:
-            db.session.commit()
-        except IntegrityError as e:
-            db.session.rollback()
-            current_app.logger.error(
-                "Attempt to create a source with duplicate codename: %s" %
-                (e,))
-
-            # Issue 2386: don't log in on duplicates
-            del session['codename']
-
-            # Issue 4361: Delete 'logged_in' if it's in the session
-            try:
-                del session['logged_in']
-            except KeyError:
-                pass
-
-            abort(500)
+        if session.get('logged_in', False):
+            flash(gettext("You are already logged in. Please verify your codename below as it " +
+                          "may differ from the one displayed on the previous page."),
+                  'notification')
         else:
-            os.mkdir(current_app.storage.path(filesystem_id))
+            tab_id = request.form['tab_id']
+            codename = session['codenames'][tab_id]
+            session['codename'] = codename
+
+            del session['codenames']
+
+            filesystem_id = current_app.crypto_util.hash_codename(codename)
+
+            source = Source(filesystem_id, current_app.crypto_util.display_id())
+            db.session.add(source)
+            try:
+                db.session.commit()
+            except IntegrityError as e:
+                db.session.rollback()
+                current_app.logger.error(
+                    "Attempt to create a source with duplicate codename: %s" %
+                    (e,))
+
+                # Issue 2386: don't log in on duplicates
+                del session['codename']
+
+                # Issue 4361: Delete 'logged_in' if it's in the session
+                try:
+                    del session['logged_in']
+                except KeyError:
+                    pass
+
+                abort(500)
+            else:
+                os.mkdir(current_app.storage.path(filesystem_id))
 
-        session['logged_in'] = True
+            session['logged_in'] = True
         return redirect(url_for('.lookup'))
 
     @view.route('/lookup', methods=('GET',))
diff --git a/securedrop/source_templates/generate.html b/securedrop/source_templates/generate.html
index 51136ad8b6..4be2171061 100644
--- a/securedrop/source_templates/generate.html
+++ b/securedrop/source_templates/generate.html
@@ -38,6 +38,7 @@ <h1>{{ gettext('Welcome') }}</h1>
 
 <form id="create-form" method="post" action="/create" autocomplete="off">
   <input name="csrf_token" type="hidden" value="{{ csrf_token() }}">
+  <input name="tab_id" type="hidden" value="{{ tab_id }}">
   <button type="submit" class="btn--space pull-right" id="continue-button">
      {{ gettext('SUBMIT DOCUMENTS') }}
   </button>
diff --git a/securedrop/tests/functional/source_navigation_steps.py b/securedrop/tests/functional/source_navigation_steps.py
index edc94c65cc..3778c30dc0 100644
--- a/securedrop/tests/functional/source_navigation_steps.py
+++ b/securedrop/tests/functional/source_navigation_steps.py
@@ -40,6 +40,9 @@ def _source_clicks_submit_documents_on_homepage(self):
         # a diceware codename they can use for subsequent logins
         assert self._is_on_generate_page()
 
+    def _source_regenerates_codename(self):
+        self.safe_click_by_id("regenerate-submit")
+
     def _source_chooses_to_submit_documents(self):
         self._source_clicks_submit_documents_on_homepage()
 
@@ -48,7 +51,7 @@ def _source_chooses_to_submit_documents(self):
         assert len(codename.text) > 0
         self.source_name = codename.text
 
-    def _source_shows_codename(self):
+    def _source_shows_codename(self, verify_source_name=True):
         content = self.driver.find_element_by_id("codename-hint-content")
         assert not content.is_displayed()
 
@@ -57,7 +60,8 @@ def _source_shows_codename(self):
         self.wait_for(lambda: content.is_displayed())
         assert content.is_displayed()
         content_content = self.driver.find_element_by_css_selector("#codename-hint-content p")
-        assert content_content.text == self.source_name
+        if verify_source_name:
+            assert content_content.text == self.source_name
 
     def _source_hides_codename(self):
         content = self.driver.find_element_by_id("codename-hint-content")
@@ -223,3 +227,17 @@ def _source_sees_document_attachment_item(self):
     def _source_does_not_sees_document_attachment_item(self):
         with pytest.raises(NoSuchElementException):
             self.driver.find_element_by_class_name("attachment")
+
+    def _source_sees_already_logged_in_in_other_tab_message(self):
+        notification = self.driver.find_element_by_css_selector(".notification")
+
+        if not hasattr(self, "accepted_languages"):
+            expected_text = "You are already logged in."
+            assert expected_text in notification.text
+
+    def _source_sees_redirect_already_logged_in_message(self):
+        notification = self.driver.find_element_by_css_selector(".notification")
+
+        if not hasattr(self, "accepted_languages"):
+            expected_text = "You were redirected because you are already logged in."
+            assert expected_text in notification.text
diff --git a/securedrop/tests/functional/test_source.py b/securedrop/tests/functional/test_source.py
index f6f734d006..8063d12a5e 100644
--- a/securedrop/tests/functional/test_source.py
+++ b/securedrop/tests/functional/test_source.py
@@ -29,3 +29,106 @@ def test_journalist_key_from_source_interface(self):
 
         data = data.decode('utf-8')
         assert "BEGIN PGP PUBLIC KEY BLOCK" in data
+
+
+class TestDuplicateSourceInterface(
+        functional_test.FunctionalTest,
+        source_navigation_steps.SourceNavigationStepsMixin):
+
+    def get_codename_generate(self):
+        return self.driver.find_element_by_css_selector("#codename").text
+
+    def get_codename_lookup(self):
+        return self.driver.find_element_by_css_selector("#codename-hint-content p").text
+
+    def test_duplicate_generate_pages(self):
+        # Test generation of multiple codenames in different browser tabs, ref. issue 4458.
+
+        # Generate a codename in Tab A
+        assert len(self.driver.window_handles) == 1
+        tab_a = self.driver.current_window_handle
+        self._source_visits_source_homepage()
+        self._source_chooses_to_submit_documents()
+        codename_a = self.get_codename_generate()
+
+        # Generate a different codename in Tab B
+        self.driver.execute_script("window.open()")
+        tab_b = self.driver.window_handles[1]
+        self.driver.switch_to.window(tab_b)
+        assert self.driver.current_window_handle == tab_b
+        self._source_visits_source_homepage()
+        self._source_chooses_to_submit_documents()
+        codename_b = self.get_codename_generate()
+
+        assert tab_a != tab_b
+        assert codename_a != codename_b
+
+        # Proceed to submit documents in Tab A
+        self.driver.switch_to.window(tab_a)
+        assert self.driver.current_window_handle == tab_a
+        self._source_continues_to_submit_page()
+        assert self._is_on_lookup_page()
+        self._source_shows_codename(verify_source_name=False)
+        codename_lookup_a = self.get_codename_lookup()
+        assert codename_lookup_a == codename_a
+        self._source_submits_a_message()
+
+        # Proceed to submit documents in Tab B
+        self.driver.switch_to.window(tab_b)
+        assert self.driver.current_window_handle == tab_b
+        self._source_continues_to_submit_page()
+        assert self._is_on_lookup_page()
+        self._source_sees_already_logged_in_in_other_tab_message()
+        self._source_shows_codename(verify_source_name=False)
+        codename_lookup_b = self.get_codename_lookup()
+        # We expect the codename to be the one from Tab A
+        assert codename_lookup_b == codename_a
+        self._source_submits_a_message()
+
+    def test_duplicate_generate_pages_with_refresh(self):
+        # Test generation of multiple codenames in different browser tabs, including behavior
+        # of refreshing the codemae in each tab. Ref. issue 4458.
+
+        # Generate a codename in Tab A
+        assert len(self.driver.window_handles) == 1
+        tab_a = self.driver.current_window_handle
+        self._source_visits_source_homepage()
+        self._source_chooses_to_submit_documents()
+        codename_a1 = self.get_codename_generate()
+        # Regenerate codename in Tab A
+        self._source_regenerates_codename()
+        codename_a2 = self.get_codename_generate()
+        assert codename_a1 != codename_a2
+
+        # Generate a different codename in Tab B
+        self.driver.execute_script("window.open()")
+        tab_b = self.driver.window_handles[1]
+        self.driver.switch_to.window(tab_b)
+        assert self.driver.current_window_handle == tab_b
+        self._source_visits_source_homepage()
+        self._source_chooses_to_submit_documents()
+        codename_b = self.get_codename_generate()
+        assert codename_b != codename_a1 != codename_a2
+
+        # Proceed to submit documents in Tab A
+        self.driver.switch_to.window(tab_a)
+        assert self.driver.current_window_handle == tab_a
+        self._source_continues_to_submit_page()
+        assert self._is_on_lookup_page()
+        self._source_shows_codename(verify_source_name=False)
+        codename_lookup_a = self.get_codename_lookup()
+        assert codename_lookup_a == codename_a2
+        self._source_submits_a_message()
+
+        # Regenerate codename in Tab B
+        self.driver.switch_to.window(tab_b)
+        assert self.driver.current_window_handle == tab_b
+        self._source_regenerates_codename()
+        # We expect the source to be directed to /lookup with a flash message
+        assert self._is_on_lookup_page()
+        self._source_sees_redirect_already_logged_in_message()
+        # Check codename
+        self._source_shows_codename(verify_source_name=False)
+        codename_lookup_b = self.get_codename_lookup()
+        assert codename_lookup_b == codename_a2
+        self._source_submits_a_message()
diff --git a/securedrop/tests/test_integration.py b/securedrop/tests/test_integration.py
index cb2fb0e944..971a1ac4bf 100644
--- a/securedrop/tests/test_integration.py
+++ b/securedrop/tests/test_integration.py
@@ -56,7 +56,8 @@ def test_submit_message(source_app, journalist_app, test_journo):
 
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create', follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id}, follow_redirects=True)
         filesystem_id = g.filesystem_id
         # redirected to submission form
         resp = app.post('/submit', data=dict(
@@ -153,7 +154,8 @@ def test_submit_file(source_app, journalist_app, test_journo):
 
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create', follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id}, follow_redirects=True)
         filesystem_id = g.filesystem_id
         # redirected to submission form
         resp = app.post('/submit', data=dict(
@@ -254,7 +256,8 @@ def _helper_test_reply(journalist_app, source_app, config, test_journo,
 
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create', follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id}, follow_redirects=True)
         codename = session['codename']
         filesystem_id = g.filesystem_id
         # redirected to submission form
@@ -474,7 +477,8 @@ def test_delete_collection(mocker, source_app, journalist_app, test_journo):
     # first, add a source
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create')
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id})
         resp = app.post('/submit', data=dict(
             msg="This is a test.",
             fh=(BytesIO(b''), ''),
@@ -523,7 +527,8 @@ def test_delete_collections(mocker, journalist_app, source_app, test_journo):
         num_sources = 2
         for i in range(num_sources):
             app.get('/generate')
-            app.post('/create')
+            tab_id = next(iter(session['codenames'].keys()))
+            app.post('/create', data={'tab_id': tab_id})
             app.post('/submit', data=dict(
                 msg="This is a test " + str(i) + ".",
                 fh=(BytesIO(b''), ''),
@@ -577,7 +582,8 @@ def test_filenames(source_app, journalist_app, test_journo):
     # add a source and submit stuff
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create')
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id})
         _helper_filenames_submit(app)
 
     # navigate to the collection page
@@ -603,7 +609,8 @@ def test_filenames_delete(journalist_app, source_app, test_journo):
     # add a source and submit stuff
     with source_app.test_client() as app:
         app.get('/generate')
-        app.post('/create')
+        tab_id = next(iter(session['codenames'].keys()))
+        app.post('/create', data={'tab_id': tab_id})
         _helper_filenames_submit(app)
 
     # navigate to the collection page
@@ -714,7 +721,8 @@ def test_prevent_document_uploads(source_app, journalist_app, test_admin):
     # Check that the source interface accepts only messages:
     with source_app.test_client() as app:
         app.get('/generate')
-        resp = app.post('/create', follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        resp = app.post('/create', data={'tab_id': tab_id}, follow_redirects=True)
         assert resp.status_code == 200
 
         text = resp.data.decode('utf-8')
@@ -739,7 +747,8 @@ def test_no_prevent_document_uploads(source_app, journalist_app, test_admin):
     # Check that the source interface accepts both files and messages:
     with source_app.test_client() as app:
         app.get('/generate')
-        resp = app.post('/create', follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        resp = app.post('/create', data={'tab_id': tab_id}, follow_redirects=True)
         assert resp.status_code == 200
 
         text = resp.data.decode('utf-8')
diff --git a/securedrop/tests/test_source.py b/securedrop/tests/test_source.py
index 7cf06ae7f4..c74bbdd6bd 100644
--- a/securedrop/tests/test_source.py
+++ b/securedrop/tests/test_source.py
@@ -83,7 +83,7 @@ def test_generate(source_app):
     with source_app.test_client() as app:
         resp = app.get(url_for('main.generate'))
         assert resp.status_code == 200
-        session_codename = session['codename']
+        session_codename = next(iter(session['codenames'].values()))
 
     text = resp.data.decode('utf-8')
     assert "This codename is what you will use in future visits" in text
@@ -113,11 +113,13 @@ def test_create_new_source(source_app):
     with source_app.test_client() as app:
         resp = app.get(url_for('main.generate'))
         assert resp.status_code == 200
-        resp = app.post(url_for('main.create'), follow_redirects=True)
+        tab_id = next(iter(session['codenames'].keys()))
+        resp = app.post(url_for('main.create'), data={'tab_id': tab_id}, follow_redirects=True)
         assert session['logged_in'] is True
         # should be redirected to /lookup
         text = resp.data.decode('utf-8')
         assert "Submit Files" in text
+        assert 'codenames' not in session
 
 
 def test_generate_too_long_codename(source_app):
@@ -143,17 +145,18 @@ def test_create_duplicate_codename_logged_in_not_in_session(source_app):
         with source_app.test_client() as app:
             resp = app.get(url_for('main.generate'))
             assert resp.status_code == 200
+            tab_id = next(iter(session['codenames'].keys()))
 
             # Create a source the first time
-            resp = app.post(url_for('main.create'), follow_redirects=True)
+            resp = app.post(url_for('main.create'), data={'tab_id': tab_id}, follow_redirects=True)
             assert resp.status_code == 200
             codename = session['codename']
 
         with source_app.test_client() as app:
             # Attempt to add the same source
             with app.session_transaction() as sess:
-                sess['codename'] = codename
-            resp = app.post(url_for('main.create'), follow_redirects=True)
+                sess['codenames'] = {tab_id: codename}
+            resp = app.post(url_for('main.create'), data={'tab_id': tab_id}, follow_redirects=True)
             logger.assert_called_once()
             assert ("Attempt to create a source with duplicate codename"
                     in logger.call_args[0][0])
@@ -163,26 +166,31 @@ def test_create_duplicate_codename_logged_in_not_in_session(source_app):
 
 
 def test_create_duplicate_codename_logged_in_in_session(source_app):
-    with patch.object(source.app.logger, 'error') as logger:
-        with source_app.test_client() as app:
-            resp = app.get(url_for('main.generate'))
-            assert resp.status_code == 200
-
-            # Create a source the first time
-            resp = app.post(url_for('main.create'), follow_redirects=True)
-            assert resp.status_code == 200
+    with source_app.test_client() as app:
+        resp = app.get(url_for('main.generate'))
+        assert resp.status_code == 200
+        tab_id = next(iter(session['codenames'].keys()))
 
-            # Attempt to add the same source
-            resp = app.post(url_for('main.create'), follow_redirects=True)
-            logger.assert_called_once()
-            assert ("Attempt to create a source with duplicate codename"
-                    in logger.call_args[0][0])
-            assert resp.status_code == 500
-            assert 'codename' not in session
+        # Create a source the first time
+        resp = app.post(url_for('main.create'), data={'tab_id': tab_id}, follow_redirects=True)
+        assert resp.status_code == 200
+        codename = session['codename']
+        logged_in = session['logged_in']
 
-            # Reproducer for bug #4361
-            resp = app.post(url_for('main.index'), follow_redirects=True)
-            assert 'logged_in' not in session
+    # Attempt to add another source in the same session
+    with source_app.test_client() as app:
+        resp = app.get(url_for('main.generate'))
+        assert resp.status_code == 200
+        tab_id = next(iter(session['codenames'].keys()))
+        with app.session_transaction() as sess:
+            sess['codename'] = codename
+            sess['logged_in'] = logged_in
+        resp = app.post(url_for('main.create'), data={'tab_id': tab_id}, follow_redirects=True)
+        assert resp.status_code == 200
+        assert session['codename'] == codename
+        text = resp.data.decode('utf-8')
+        assert "You are already logged in." in text
+        assert "Submit Files" in text
 
 
 def test_lookup(source_app):
diff --git a/securedrop/tests/utils/db_helper.py b/securedrop/tests/utils/db_helper.py
index e598561c4b..bb2f14761a 100644
--- a/securedrop/tests/utils/db_helper.py
+++ b/securedrop/tests/utils/db_helper.py
@@ -173,6 +173,6 @@ def new_codename(client, session):
     """Helper function to go through the "generate codename" flow.
     """
     client.get('/generate')
-    codename = session['codename']
-    client.post('/create')
+    tab_id, codename = next(iter(session['codenames'].items()))
+    client.post('/create', data={'tab_id': tab_id})
     return codename