diff --git a/layerindex/views.py b/layerindex/views.py
index 73a4f6a..dea0a98 100644
--- a/layerindex/views.py
+++ b/layerindex/views.py
@@ -1902,6 +1902,19 @@ class BranchCompareView(FormView):
                 changed.append(recipe)
         return added, changed, removed
 
+    def get_layer_ids(self):
+        # 'layers' is a comma-separated list of layer ids (also accept it
+        # repeated); ignore anything that isn't a selectable layer
+        valid_ids = set(LayerItem.objects.filter(status__in=['P', 'X']).values_list('id', flat=True))
+        values = self.request.GET.getlist('layers') or [str(LayerItem.objects.get(name=settings.CORE_LAYER_NAME).id)]
+        layer_ids = []
+        for value in values:
+            for layer_id in value.split(','):
+                layer_id = layer_id.strip()
+                if layer_id.isdigit() and int(layer_id) in valid_ids and int(layer_id) not in layer_ids:
+                    layer_ids.append(int(layer_id))
+        return layer_ids
+
     def form_valid(self, form):
         return HttpResponseRedirect(reverse_lazy('branch_comparison', args=(form.cleaned_data['from_branch'].name, form.cleaned_data['to_branch'].name)))
 
@@ -1913,7 +1926,7 @@ class BranchCompareView(FormView):
         to_branch_id = self.request.GET.get('to_branch', None)
         if to_branch_id is not None:
             initial['to_branch'] = get_object_or_404(Branch, id=to_branch_id)
-        initial['layers'] = self.request.GET.get('layers', str(LayerItem.objects.get(name=settings.CORE_LAYER_NAME).id))
+        initial['layers'] = ','.join(str(i) for i in self.get_layer_ids())
         return initial
 
     def get_context_data(self, **kwargs):
@@ -1921,7 +1934,7 @@ class BranchCompareView(FormView):
         from_branch_id = self.request.GET.get('from_branch', None)
         to_branch_id = self.request.GET.get('to_branch', None)
 
-        layer_ids = self.request.GET.get('layers', str(LayerItem.objects.get(name=settings.CORE_LAYER_NAME).id))
+        layer_ids = self.get_layer_ids()
         from_branch = None
         if from_branch_id is not None:
             from_branch = get_object_or_404(Branch, id=from_branch_id)
@@ -1936,7 +1949,7 @@ class BranchCompareView(FormView):
         context['layers'] = LayerItem.objects.filter(status__in=['P', 'X']).order_by('name')
         context['showlayers'] = layer_ids
         layerlist = dict(context['layers'].values_list('id', 'name'))
-        context['showlayers_text'] = ', '.join([layerlist[int(i)] for i in layer_ids])
+        context['showlayers_text'] = ', '.join([layerlist[i] for i in layer_ids])
 
         return context
 
diff --git a/tests/test_branch_compare_view.py b/tests/test_branch_compare_view.py
new file mode 100644
index 0000000..6211c5f
--- /dev/null
+++ b/tests/test_branch_compare_view.py
@@ -0,0 +1,109 @@
+# layerindex-web - tests for BranchCompareView
+#
+# Copyright (C) 2026 Tim Orling <tim.orling@konsulko.com>
+#
+# Licensed under the MIT license, see COPYING.MIT for details
+#
+# SPDX-License-Identifier: MIT
+
+# Tests for bug #15332 - Branch Comparison throws Internal Server Error
+# https://bugzilla.yoctoproject.org/show_bug.cgi?id=15332
+#
+# The 'layers' parameter is a comma-separated list of layer ids, but the view
+# iterated over the raw string character by character. So layers=59 selected
+# layers 5 and 9, and layers=59,1 tried to look up a layer with id ','.
+
+import pytest
+from django.test import TestCase
+from django.urls import reverse
+
+from layerindex.models import Branch, LayerItem, LayerBranch, Recipe
+
+
+@pytest.mark.django_db
+class TestBranchCompareView(TestCase):
+    """Tests for BranchCompareView layer selection (bug #15332)."""
+
+    def setUp(self):
+        self.from_branch = Branch.objects.create(
+            name='old', bitbake_branch='old', short_description='Old',
+            sort_priority=2)
+        self.to_branch = Branch.objects.create(
+            name='new', bitbake_branch='new', short_description='New',
+            sort_priority=1)
+
+        # Explicit ids so that '59' would be misread as layers 5 and 9
+        self.layers = {}
+        for layer_id, name in ((1, 'openembedded-core'), (5, 'meta-five'),
+                               (9, 'meta-nine'), (59, 'meta-fiftynine')):
+            layer = LayerItem.objects.create(
+                id=layer_id, name=name, status='P', layer_type='S',
+                summary=name, description=name,
+                vcs_url='git://example.com/%s.git' % name)
+            self.layers[layer_id] = layer
+            for branch, pv in ((self.from_branch, '1.0'), (self.to_branch, '2.0')):
+                lb = LayerBranch.objects.create(layer=layer, branch=branch)
+                Recipe.objects.create(
+                    layerbranch=lb, filename='%s_%s.bb' % (name, pv),
+                    pn='%s-recipe' % name, pv=pv, filepath='recipes-test')
+
+    def _get(self, query='', url_name='branch_comparison'):
+        url = '%s?from_branch=%d&to_branch=%d%s' % (
+            reverse(url_name), self.from_branch.id, self.to_branch.id, query)
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 200)
+        return response
+
+    def _changed_pns(self, response):
+        return sorted(r.pn for r in response.context['changed'])
+
+    def test_default_is_core_layer(self):
+        response = self._get()
+        self.assertEqual(self._changed_pns(response), ['openembedded-core-recipe'])
+
+    def test_multi_digit_layer_id(self):
+        response = self._get('&layers=59')
+        self.assertEqual(self._changed_pns(response), ['meta-fiftynine-recipe'])
+        self.assertEqual(response.context['showlayers_text'], 'meta-fiftynine')
+
+    def test_multiple_layers(self):
+        response = self._get('&layers=59%2C1')
+        self.assertEqual(self._changed_pns(response),
+                         ['meta-fiftynine-recipe', 'openembedded-core-recipe'])
+
+    def test_repeated_layers_param(self):
+        response = self._get('&layers=59&layers=1')
+        self.assertEqual(self._changed_pns(response),
+                         ['meta-fiftynine-recipe', 'openembedded-core-recipe'])
+
+    def test_legacy_url_with_l_params(self):
+        # URL as previously generated by the form, with the checkbox values
+        # also submitted as 'l'
+        response = self._get('&layers=59%2C1&l=59&l=1')
+        self.assertEqual(self._changed_pns(response),
+                         ['meta-fiftynine-recipe', 'openembedded-core-recipe'])
+
+    def test_invalid_layer_ids_ignored(self):
+        response = self._get('&layers=59%2C%2Cbogus%2C9999')
+        self.assertEqual(self._changed_pns(response), ['meta-fiftynine-recipe'])
+
+    def test_badge_and_checkboxes_match_selection(self):
+        response = self._get('&layers=59%2C1')
+        self.assertContains(response, 'id="id_layers_count">2</span>', html=False)
+        content = response.content.decode()
+        for layer_id in (1, 59):
+            self.assertRegex(content, r'id="id_layercheckbox_%d"\s+checked' % layer_id)
+        for layer_id in (5, 9):
+            self.assertNotRegex(content, r'id="id_layercheckbox_%d"\s+checked' % layer_id)
+        # Checkboxes must not be submitted alongside the hidden 'layers' field
+        self.assertNotContains(response, 'name="l"')
+
+    def test_plain_text_output(self):
+        response = self._get('&layers=59%2C1', url_name='branch_comparison_plain')
+        self.assertContains(response, '(layers: meta-fiftynine, openembedded-core)')
+
+    def test_from_branch_only(self):
+        url = '%s?from_branch=%d' % (reverse('branch_comparison'), self.from_branch.id)
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 200)
+        self.assertIsNone(response.context['to_branch'])