diff --git a/cibuildwheel/linux.py b/cibuildwheel/linux.py
index 64ccda93..e81e231a 100644
--- a/cibuildwheel/linux.py
+++ b/cibuildwheel/linux.py
@@ -103,7 +103,7 @@ def build(project_dir, package_name, output_dir, test_command, test_requires, be
             pybin_paths=' '.join(c.path+'/bin' for c in platform_configs),
             test_requires=' '.join(test_requires),
             test_command=shlex_quote(
-                test_command.format(python='python', pip='pip', project='/project') if test_command else ''
+                prepare_command(test_command, python='python', pip='pip', project='/project') if test_command else ''
             ),
             before_build=shlex_quote(
                 prepare_command(before_build, python='python', pip='pip', project='/project') if before_build else ''