diff --git a/unittest/force-styles/test_fix_timestep.cpp b/unittest/force-styles/test_fix_timestep.cpp
index 64aa54e96b..981bc46eef 100644
--- a/unittest/force-styles/test_fix_timestep.cpp
+++ b/unittest/force-styles/test_fix_timestep.cpp
@@ -203,9 +203,8 @@ void generate_yaml_file(const char *outfile, const TestConfig &config)
         // run_stress, if enabled
         if (fix->thermo_virial) {
             auto stress = fix->virial;
-            block       = fmt::format("{:23.16e} {:23.16e} {:23.16e} "
-                                "{:23.16e} {:23.16e} {:23.16e}",
-                                stress[0], stress[1], stress[2], stress[3], stress[4], stress[5]);
+            block       = fmt::format("{:23.16e} {:23.16e} {:23.16e} {:23.16e} {:23.16e} {:23.16e}",
+                                      stress[0], stress[1], stress[2], stress[3], stress[4], stress[5]);
             writer.emit_block("run_stress", block);
         }