diff --git a/esphome/components/thermostat/thermostat_climate.cpp b/esphome/components/thermostat/thermostat_climate.cpp
index d2f5db3b32..8258fa9d65 100644
--- a/esphome/components/thermostat/thermostat_climate.cpp
+++ b/esphome/components/thermostat/thermostat_climate.cpp
@@ -1197,6 +1197,9 @@ void ThermostatClimate::change_custom_preset_(const std::string &custom_preset)
     } else {
       ESP_LOGI(TAG, "No changes required to apply custom preset %s", custom_preset.c_str());
     }
+    // Note: set_custom_preset_() above handles preset.reset() and custom_preset_ assignment internally.
+    // The old code had these lines here unconditionally, which was a bug (double assignment, state modification
+    // even when no changes were needed). Now properly handled by the protected setter with mutual exclusion.
   } else {
     ESP_LOGW(TAG, "Custom preset %s not configured; ignoring", custom_preset.c_str());
   }