--- a/taskcluster/taskgraph/transforms/repackage_signing.py
+++ b/taskcluster/taskgraph/transforms/repackage_signing.py
@@ -5,17 +5,17 @@
 Transform the repackage signing task into an actual task description.
 """
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 from taskgraph.transforms.base import TransformSequence
 from taskgraph.util.attributes import copy_attributes_from_dependent_job
 from taskgraph.util.schema import validate_schema, Schema
-from taskgraph.util.scriptworker import get_signing_cert_scope
+from taskgraph.util.scriptworker import get_signing_cert_scope_per_platform
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
 # Voluptuous uses marker objects as dictionary *keys*, but they are not
 # comparable, so we cast all of the keys back to regular strings
 task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
 
 transforms = TransformSequence()
@@ -72,40 +72,44 @@ def make_repackage_signing_description(c
         attributes['repackage_type'] = 'repackage-signing'
 
         locale_str = ""
         if dep_job.attributes.get('locale'):
             treeherder['symbol'] = 'tc-rs({})'.format(dep_job.attributes.get('locale'))
             attributes['locale'] = dep_job.attributes.get('locale')
             locale_str = "{}/".format(dep_job.attributes.get('locale'))
 
-        scopes = [get_signing_cert_scope(config),
-                  "project:releng:signing:format:mar_sha384"]
+        build_platform = dep_job.attributes.get('build_platform')
+        is_nightly = dep_job.attributes.get('nightly')
+        signing_cert_scope = get_signing_cert_scope_per_platform(
+            build_platform, is_nightly, config
+        )
+        scopes = [signing_cert_scope, 'project:releng:signing:format:mar_sha384']
 
         upstream_artifacts = [{
             "taskId": {"task-reference": "<repackage>"},
             "taskType": "repackage",
             "paths": [
                 "public/build/{}target.complete.mar".format(locale_str),
             ],
             "formats": ["mar_sha384"]
         }]
-        if 'win' in dep_job.attributes.get('build_platform'):
+        if 'win' in build_platform:
             upstream_artifacts.append({
                 "taskId": {"task-reference": "<repackage>"},
                 "taskType": "repackage",
                 "paths": [
                     "public/build/{}target.installer.exe".format(locale_str),
                 ],
                 "formats": ["sha2signcode"]
             })
             scopes.append("project:releng:signing:format:sha2signcode")
 
             # Stub installer is only generated on win32
-            if '32' in dep_job.attributes.get('build_platform'):
+            if '32' in build_platform:
                 upstream_artifacts.append({
                     "taskId": {"task-reference": "<repackage>"},
                     "taskType": "repackage",
                     "paths": [
                         "public/build/{}target.stub-installer.exe".format(locale_str),
                     ],
                     "formats": ["sha2signcodestub"]
                 })
@@ -125,17 +129,16 @@ def make_repackage_signing_description(c
             'treeherder': treeherder,
         }
 
         funsize_platforms = [
             'macosx64-nightly',
             'win32-nightly',
             'win64-nightly'
         ]
-        if dep_job.attributes.get('build_platform') in funsize_platforms and \
-                dep_job.attributes.get('nightly'):
+        if build_platform in funsize_platforms and is_nightly:
             route_template = "project.releng.funsize.level-{level}.{project}"
             task['routes'] = [
                 route_template.format(project=config.params['project'],
                                       level=config.params['level'])
             ]
 
         yield task

--- a/taskcluster/taskgraph/transforms/signing.py
+++ b/taskcluster/taskgraph/transforms/signing.py
@@ -5,17 +5,17 @@
 Transform the signing task into an actual task description.
 """
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 from taskgraph.transforms.base import TransformSequence
 from taskgraph.util.attributes import copy_attributes_from_dependent_job
 from taskgraph.util.schema import validate_schema, Schema
-from taskgraph.util.scriptworker import get_signing_cert_scope, get_devedition_signing_cert_scope
+from taskgraph.util.scriptworker import get_signing_cert_scope_per_platform
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Any, Required, Optional
 
 
 # Voluptuous uses marker objects as dictionary *keys*, but they are not
 # comparable, so we cast all of the keys back to regular strings
 task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
 
@@ -112,26 +112,19 @@ def make_task_description(config, jobs):
 
         attributes = copy_attributes_from_dependent_job(dep_job)
         attributes['signed'] = True
 
         if dep_job.attributes.get('chunk_locales'):
             # Used for l10n attribute passthrough
             attributes['chunk_locales'] = dep_job.attributes.get('chunk_locales')
 
-        # This code wasn't originally written with the possibility of using different
-        # signing cert scopes for different platforms on the same branch. This isn't
-        # ideal, but it's what we currently have to make this possible.
-        if dep_job.attributes.get('build_platform') in set(
-          ['linux64-devedition-nightly', 'linux-devedition-nightly']):
-            signing_cert_scope = get_devedition_signing_cert_scope(config)
-        elif is_nightly:
-            signing_cert_scope = get_signing_cert_scope(config)
-        else:
-            signing_cert_scope = 'project:releng:signing:cert:dep-signing'
+        signing_cert_scope = get_signing_cert_scope_per_platform(
+            dep_job.attributes.get('build_platform'), is_nightly, config
+        )
 
         task = {
             'label': label,
             'description': description,
             'worker-type': _generate_worker_type(signing_cert_scope),
             'worker': {'implementation': 'scriptworker-signing',
                        'upstream-artifacts': job['upstream-artifacts'],
                        'max-run-time': 3600},

--- a/taskcluster/taskgraph/util/scriptworker.py
+++ b/taskcluster/taskgraph/util/scriptworker.py
@@ -414,8 +414,21 @@ def get_release_config(config):
         build_number = str(os.environ.get("BUILD_NUMBER", ""))
         if not build_number.isdigit():
             raise ValueError("Release graphs must specify `BUILD_NUMBER` in the environment!")
         release_config['build_number'] = int(build_number)
         with open(VERSION_PATH, "r") as fh:
             version = fh.readline().rstrip()
         release_config['version'] = version
     return release_config
+
+
+def get_signing_cert_scope_per_platform(build_platform, is_nightly, config):
+    if build_platform in (
+        'linux-devedition-nightly', 'linux64-devedition-nightly',
+        'macosx64-devedition-nightly',
+        'win32-devedition-nightly', 'win64-devedition-nightly',
+    ):
+        return get_devedition_signing_cert_scope(config)
+    elif is_nightly:
+        return get_signing_cert_scope(config)
+    else:
+        return 'project:releng:signing:cert:dep-signing'