diff --git a/src/osx/smc.cpp b/src/osx/smc.cpp
index 95d75f0..ace9ce6 100644
--- a/src/osx/smc.cpp
+++ b/src/osx/smc.cpp
@@ -18,6 +18,9 @@ tab-size = 4
 
 #include "smc.hpp"
 
+static constexpr size_t MaxIndexCount = sizeof("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ") - 1;
+static constexpr const char *KeyIndexes = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
 static UInt32 _strtoul(char *str, int size, int base) {
 	UInt32 total = 0;
 	int i;
@@ -91,13 +94,16 @@ namespace Cpu {
 	// according to VirtualSMC docs (hackintosh fake SMC) the enumeration follows with alphabetic chars - not implemented yet here (nor in VirtualSMC)
 	long long SMCConnection::getTemp(int core) {
 		char key[] = SMC_KEY_CPU_TEMP;
+		if (core > MaxIndexCount) {
+			return -1;
+		}
 		if (core >= 0) {
-			snprintf(key, 5, "TC%1dc", core);
+			snprintf(key, 5, "TC%1cc", KeyIndexes[core]);
 		}
 		long long result = getSMCTemp(key);
 		if (result == -1) {
 			// try again with C
-			snprintf(key, 5, "TC%1dC", core);
+			snprintf(key, 5, "TC%1dC", KeyIndexes[core]);
 			result = getSMCTemp(key);
 		}
 		return result;