diff --git a/MHZ.cpp b/MHZ.cpp
index b7942f1..b3081c9 100644
--- a/MHZ.cpp
+++ b/MHZ.cpp
@@ -14,8 +14,8 @@ const int MHZ_10K = 3;
 const unsigned long MHZ14A_PREHEATING_TIME = 3L * 60L * 1000L;
 const unsigned long MHZ19B_PREHEATING_TIME = 3L * 60L * 1000L;
 
-const unsigned long MHZ14A_RESPONSE_TIME = 60 * 1000;
-const unsigned long MHZ19B_RESPONSE_TIME = 120 * 1000;
+const unsigned long MHZ14A_RESPONSE_TIME = (unsigned long)60 * 1000;
+const unsigned long MHZ19B_RESPONSE_TIME = (unsigned long)120 * 1000;
 
 const int STATUS_NO_RESPONSE = -2;
 const int STATUS_CHECKSUM_MISMATCH = -3;
@@ -286,7 +286,7 @@ void MHZ::setRange(int range) //only available for MHZ-19B < 1.6 and MH-Z 14a
 
 void MHZ::calibrateZero()
 {
-  char cmd[9] = {0xFF, 0x01, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78};
+  uint8_t cmd[9] = {0xFF, 0x01, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78};
   _serial->write(cmd,9);
 }
 
diff --git a/README.md b/README.md
index d4e9491..d478be8 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # MH-Z14A, MH-Z19B CO2 ... Module
 
-Arduino implementation for MH-Z CO2 sensors such as **MH-Z14A**, **MH-Z18B** (as I didn't find all info in one place).
+Arduino implementation for MH-Z CO2 sensors such as **MH-Z14A**, **MH-Z19B** (as I didn't find all info in one place).
 
 The sensor is available for ~20 bucks at the usual places.