diff --git a/peru/runtime.py b/peru/runtime.py
index d8e2410..d53f3b4 100644
--- a/peru/runtime.py
+++ b/peru/runtime.py
@@ -85,11 +85,17 @@ def _set_paths(self, args, env):
             self.peru_file = find_project_file(os.getcwd(), basename)
             self.sync_dir = os.path.dirname(self.peru_file)
 
-        self.state_dir = os.path.abspath(
-            args['--state-dir']) if args['--state-dir'] else os.path.join(self.sync_dir, '.peru')
+        if args['--state-dir']:
+            self.state_dir = os.path.abspath(args['--state-dir'])
+        else:
+            self.state_dir = os.path.join(self.sync_dir, '.peru')
 
-        self.cache_dir = os.path.abspath(
-            args['--cache-dir']) if args['--cache-dir'] else os.path.join(self.state_dir, 'cache')
+        if args['--cache-dir']:
+            self.cache_dir = os.path.abspath(args['--cache-dir'])
+        elif env.get('PERU_CACHE_DIR'):
+            self.cache_dir = env.get('PERU_CACHE_DIR')
+        else:
+            self.cache_dir = os.path.join(self.state_dir, 'cache')
 
     def tmp_dir(self):
         dir = tempfile.TemporaryDirectory(dir=self._tmp_root)
diff --git a/tests/test_paths.py b/tests/test_paths.py
index c236d2d..95b1eaa 100644
--- a/tests/test_paths.py
+++ b/tests/test_paths.py
@@ -46,11 +46,6 @@ def test_unmodified_sync(self):
         shared.run_peru_command(['sync'], self.cwd)
         self.assert_success(self.project_dir, self.state_dir, self.cache_dir)
 
-    def test_peru_file_and_sync_dir_must_be_set_together(self):
-        for command in [['--sync-dir=junk', 'sync'], ['--file=junk', 'sync']]:
-            with self.assertRaises(CommandLineError):
-                shared.run_peru_command(command, cwd=self.cwd)
-
     def test_file_and_file_basename_incompatible(self):
         with self.assertRaises(CommandLineError):
             shared.run_peru_command([