diff --git a/cpu_darwin.go b/cpu_darwin.go
index e2c48d6..5af5635 100644
--- a/cpu_darwin.go
+++ b/cpu_darwin.go
@@ -17,6 +17,6 @@ func init() {
 	if !haveAVX512 {
 		// On some Macs, AVX512 detection is buggy, so fallback to sysctl
 		b, _ := syscall.Sysctl("hw.optional.avx512f")
-		haveAVX512 = b[0] == 1
+		haveAVX512 = len(b) > 0 && b[0] == 1
 	}
 }