diff --git a/firmware/src/config.cpp b/firmware/src/config.cpp
index 02ef1c3..ea1fefd 100644
--- a/firmware/src/config.cpp
+++ b/firmware/src/config.cpp
@@ -89,7 +89,12 @@ bool config_save_tuning(const CVTuning& tuning) {
     size_t r3 = prefs.putFloat("cv_move", tuning.max_move);
     size_t r4 = prefs.putUInt("cv_miss", (uint32_t)tuning.max_missed);
     size_t r5 = prefs.putUInt("cv_line", (uint32_t)tuning.line_offset);
+    if (!(r1 > 0 && r2 > 0 && r3 > 0 && r4 > 0 && r5 > 0)) {
+        prefs.end();
+        return false;
+    }
+    // cv_ver is the atomic commit marker: only written after all tunables succeed.
     size_t r6 = prefs.putUInt("cv_ver",  tuning.cfg_version);
     prefs.end();
-    return (r1 > 0) && (r2 > 0) && (r3 > 0) && (r4 > 0) && (r5 > 0) && (r6 > 0);
+    return r6 > 0;
 }