diff --git a/smc.c b/smc.c
index 0992962..83ac03b 100644
--- a/smc.c
+++ b/smc.c
@@ -26,8 +26,14 @@
 
 #include "smc.h"
 
+#if (MAC_OS_X_VERSION_MAX_ALLOWED < 120000) // Before macOS 12 Monterey
+  #define kIOMainPortDefault kIOMasterPortDefault
+#endif
+
 static io_connect_t conn;
 
+UInt8 coreNums[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
 UInt32 strtoulWithSize(const char *str, int size, int base) {
     UInt32 total = 0;
     int i;
@@ -56,7 +62,7 @@ kern_return_t SMCOpen(void) {
     io_object_t device;
 
     CFMutableDictionaryRef matchingDictionary = IOServiceMatching("AppleSMC");
-    result = IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDictionary, &iterator);
+    result = IOServiceGetMatchingServices(kIOMainPortDefault, matchingDictionary, &iterator);
     if (result != kIOReturnSuccess) {
         printf("Error: IOServiceGetMatchingServices() = %08x\n", result);
         return 1;
@@ -156,29 +162,29 @@ double SMCGetTemperature(char *key) {
 }
 
 int getTemperatureSMCKeySize(unsigned long core) {
-    return snprintf(NULL, 0, "%s%lu%c", SMC_CPU_CORE_TEMP_PREFIX, core, SMC_CPU_CORE_TEMP_SUFFIX_NEW);
+    return snprintf(NULL, 0, "%s%c%c", SMC_CPU_CORE_TEMP_PREFIX, coreNums[core], SMC_CPU_CORE_TEMP_SUFFIX_NEW);
 }
 
 void getOldSMCTemperatureKeyTemplate(char *key) {
-    sprintf(key, "%s%%lu%c", SMC_CPU_CORE_TEMP_PREFIX, SMC_CPU_CORE_TEMP_SUFFIX_OLD);
+    sprintf(key, "%s%%c%c", SMC_CPU_CORE_TEMP_PREFIX, SMC_CPU_CORE_TEMP_SUFFIX_OLD);
 }
 
 void getNewSMCTemperatureKeyTemplate(char *key) {
-    sprintf(key, "%s%%lu%c", SMC_CPU_CORE_TEMP_PREFIX, SMC_CPU_CORE_TEMP_SUFFIX_NEW);
+    sprintf(key, "%s%%c%c", SMC_CPU_CORE_TEMP_PREFIX, SMC_CPU_CORE_TEMP_SUFFIX_NEW);
 }
 
 double getTemperatureKeyTemplate(unsigned long core, char *templateKey) {
     getNewSMCTemperatureKeyTemplate(templateKey);
 
     char key[getTemperatureSMCKeySize(core)];
-    sprintf(key, templateKey, core);
+    sprintf(key, templateKey, coreNums[core]);
 
     double temperature = SMCGetTemperature(key);
 
     if (temperature == 0) {
         // We must use the old key
         getOldSMCTemperatureKeyTemplate(templateKey);
-        sprintf(key, templateKey, core);
+        sprintf(key, templateKey, coreNums[core]);
         temperature = SMCGetTemperature(key);
     }
 
@@ -322,7 +328,7 @@ int main(int argc, char *argv[]) {
 
             for (int i = 1; i < coreCount; ++i) {
                 char key[getTemperatureSMCKeySize(coreList[i])];
-                sprintf(key, templateKey, coreList[i]);
+                sprintf(key, templateKey, coreNums[coreList[i]]);
                 double temperature = SMCGetTemperature(key);
 
                 if (temperature == 0) {