diff --git a/percy/environment.py b/percy/environment.py
index 90f1882..491b640 100644
--- a/percy/environment.py
+++ b/percy/environment.py
@@ -251,7 +251,7 @@ def commit_sha(self):
 
     @property
     def parallel_nonce(self):
-        return os.getenv('CIRCLE_BUILD_NUM')
+        return os.getenv('CIRCLE_WORKFLOW_WORKSPACE_ID') or os.getenv('CIRCLE_BUILD_NUM')
 
     @property
     def parallel_total_shards(self):
diff --git a/tests/test_environment.py b/tests/test_environment.py
index 31e9b8e..71f0428 100644
--- a/tests/test_environment.py
+++ b/tests/test_environment.py
@@ -54,6 +54,7 @@ def clear_env_vars(self):
             'CIRCLE_SHA1',
             'CIRCLE_BRANCH',
             'CIRCLE_BUILD_NUM',
+            'CIRCLE_WORKFLOW_WORKSPACE_ID',
             'CI_PULL_REQUESTS',
             'CIRCLE_NODE_TOTAL',
 
@@ -320,6 +321,7 @@ def setup_method(self, method):
         os.environ['CIRCLE_BRANCH'] = 'circle-branch'
         os.environ['CIRCLE_SHA1'] = 'circle-commit-sha'
         os.environ['CIRCLE_BUILD_NUM'] = 'circle-build-number'
+        os.environ['CIRCLE_WORKFLOW_WORKSPACE_ID'] = 'circle-workflow-workspace-id'
         os.environ['CIRCLE_NODE_TOTAL'] = '3'
         os.environ['CI_PULL_REQUESTS'] = 'https://github.com/owner/repo-name/pull/123'
         self.environment = percy.Environment()
@@ -334,6 +336,8 @@ def test_commit_sha(self):
         assert self.environment.commit_sha == 'circle-commit-sha'
 
     def test_parallel_nonce(self):
+        assert self.environment.parallel_nonce == 'circle-workflow-workspace-id'
+        del os.environ['CIRCLE_WORKFLOW_WORKSPACE_ID']
         assert self.environment.parallel_nonce == 'circle-build-number'
 
     def test_parallel_total(self):