diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 197441dfa7..605e133000 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -623,7 +623,7 @@ func cpuinit() {
 	// Support cpu feature variables are used in code generated by the compiler
 	// to guard execution of instructions that can not be assumed to be always supported.
 	switch GOARCH {
-	case "386", "AMD64":
+	case "386", "amd64":
 		x86HasPOPCNT = cpu.X86.HasPOPCNT
 		x86HasSSE41 = cpu.X86.HasSSE41
 		x86HasFMA = cpu.X86.HasFMA