diff --git a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
--- a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
+++ b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
@@ -10,6 +10,7 @@
  */
 final class DiffusionCommitHookEngine extends Phobject {
 
+  const ENV_REPOSITORY = 'PHABRICATOR_REPOSITORY';
   const ENV_USER = 'PHABRICATOR_USER';
   const ENV_REMOTE_ADDRESS = 'PHABRICATOR_REMOTE_ADDRESS';
   const ENV_REMOTE_PROTOCOL = 'PHABRICATOR_REMOTE_PROTOCOL';
@@ -610,7 +611,7 @@
     $console = PhutilConsole::getConsole();
 
     $env = array(
-      'PHABRICATOR_REPOSITORY' => $this->getRepository()->getCallsign(),
+      self::ENV_REPOSITORY => $this->getRepository()->getPHID(),
       self::ENV_USER => $this->getViewer()->getUsername(),
       self::ENV_REMOTE_PROTOCOL => $this->getRemoteProtocol(),
       self::ENV_REMOTE_ADDRESS => $this->getRemoteAddress(),
diff --git a/src/docs/user/userguide/diffusion_hooks.diviner b/src/docs/user/userguide/diffusion_hooks.diviner
--- a/src/docs/user/userguide/diffusion_hooks.diviner
+++ b/src/docs/user/userguide/diffusion_hooks.diviner
@@ -42,7 +42,7 @@
 These additional variables will be available in the environment, in addition
 to the variables the VCS normally provides:
 
-  - `PHABRICATOR_REPOSITORY` The callsign of the repository the hook is
+  - `PHABRICATOR_REPOSITORY` The PHID of the repository the hook is
     executing for.
   - `PHABRICATOR_USER` The Phabricator username that the session is
     authenticated under.