--- a/taskcluster/taskgraph/transforms/build.py
+++ b/taskcluster/taskgraph/transforms/build.py
@@ -4,16 +4,17 @@
 """
 Apply some defaults and minor modifications to the jobs defined in the build
 kind.
 """
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 from taskgraph.transforms.base import TransformSequence
+from taskgraph.util.attributes import TRUNK_PROJECTS
 from taskgraph.util.workertypes import worker_type_implementation
 
 transforms = TransformSequence()
 
 
 @transforms.add
 def set_defaults(config, jobs):
     """Set defaults, including those that differ per worker implementation"""
@@ -47,8 +48,43 @@ def set_env(config, jobs):
     for job in jobs:
         env = config.config['args'].env
         if env:
             job_env = {}
             if 'worker' in job:
                 job_env = job['worker']['env']
             job_env.update(dict(x.split('=') for x in env))
         yield job
+
+
+@transforms.add
+def set_channel_env(config, jobs):
+    """Export the release channel name from the repo triggering this build.
+
+    This is used by the build system to tailor behavior to specific release
+    configurations.
+    """
+    project = config.params['project']
+
+    for job in jobs:
+        if project == 'try' or project in TRUNK_PROJECTS:
+            channel = 'nightly'
+        elif project == 'mozilla-beta':
+            channel = 'beta'
+        elif project == 'mozilla-release':
+            channel = 'release'
+        elif 'esr' in project:
+            # For all intents and purposes ESR uses a release channel
+            # configuration.
+            channel = 'release'
+        # Jamun is currently testing release machinery. Remove once done.
+        elif project == 'jamun':
+            channel = 'release'
+
+        # For everything else, assume a Nightly channel configuration.
+        # This is the most reasonable choice given the purposes of
+        # twigs, etc.
+        else:
+            channel = 'nightly'
+
+        job['worker']['env']['MOZ_BUILD_CHANNEL'] = channel
+
+        yield job