diff --git a/esphome/components/bl0942/bl0942.cpp b/esphome/components/bl0942/bl0942.cpp
index b408c5549c..16ad33141d 100644
--- a/esphome/components/bl0942/bl0942.cpp
+++ b/esphome/components/bl0942/bl0942.cpp
@@ -52,12 +52,12 @@ void BL0942::loop() {
     return;
   }
   if (avail < sizeof(buffer)) {
-    if (!this->rx_start_) {
+    if (!this->rx_start_.has_value()) {
       this->rx_start_ = millis();
-    } else if (millis() > this->rx_start_ + PKT_TIMEOUT_MS) {
+    } else if (millis() - *this->rx_start_ > PKT_TIMEOUT_MS) {
       ESP_LOGW(TAG, "Junk on wire. Throwing away partial message (%zu bytes)", avail);
       this->read_array((uint8_t *) &buffer, avail);
-      this->rx_start_ = 0;
+      this->rx_start_.reset();
     }
     return;
   }
@@ -67,7 +67,7 @@ void BL0942::loop() {
       this->received_package_(&buffer);
     }
   }
-  this->rx_start_ = 0;
+  this->rx_start_.reset();
 }
 
 bool BL0942::validate_checksum_(DataPacket *data) {
diff --git a/esphome/components/bl0942/bl0942.h b/esphome/components/bl0942/bl0942.h
index 10b29a72c6..3c013f86e7 100644
--- a/esphome/components/bl0942/bl0942.h
+++ b/esphome/components/bl0942/bl0942.h
@@ -140,7 +140,7 @@ class BL0942 : public PollingComponent, public uart::UARTDevice {
   uint8_t address_ = 0;
   bool reset_ = false;
   LineFrequency line_freq_ = LINE_FREQUENCY_50HZ;
-  uint32_t rx_start_ = 0;
+  optional<uint32_t> rx_start_{};
   uint32_t prev_cf_cnt_ = 0;
 
   bool validate_checksum_(DataPacket *data);