diff --git a/esphome/components/cm1106/cm1106.cpp b/esphome/components/cm1106/cm1106.cpp
index 339a1659ac..d88ea2e1da 100644
--- a/esphome/components/cm1106/cm1106.cpp
+++ b/esphome/components/cm1106/cm1106.cpp
@@ -13,7 +13,7 @@ static const uint8_t C_M1106_CMD_SET_CO2_CALIB_RESPONSE[4] = {0x16, 0x01, 0x03,
 
 uint8_t cm1106_checksum(const uint8_t *response, size_t len) {
   uint8_t crc = 0;
-  for (int i = 0; i < len - 1; i++) {
+  for (size_t i = 0; i < len - 1; i++) {
     crc -= response[i];
   }
   return crc;