diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index d224cef2a8..db2ac1f2a6 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -732,6 +732,8 @@ func runInstall(pkg string, ch chan struct{}) {
 			pathf("%s/src/runtime/funcdata.h", goroot), 0)
 		copyfile(pathf("%s/pkg/include/asm_ppc64x.h", goroot),
 			pathf("%s/src/runtime/asm_ppc64x.h", goroot), 0)
+		copyfile(pathf("%s/pkg/include/asm_amd64.h", goroot),
+			pathf("%s/src/runtime/asm_amd64.h", goroot), 0)
 	}
 
 	// Generate any missing files; regenerate existing ones.
diff --git a/src/runtime/asm_amd64.h b/src/runtime/asm_amd64.h
new file mode 100644
index 0000000000..49e0ee2323
--- /dev/null
+++ b/src/runtime/asm_amd64.h
@@ -0,0 +1,14 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Define features that are guaranteed to be supported by setting the AMD64 variable.
+// If a feature is supported, there's no need to check it at runtime every time.
+
+#ifdef GOAMD64_v3
+#define hasAVX2
+#endif
+
+#ifdef GOAMD64_v4
+#define hasAVX2
+#endif
diff --git a/src/runtime/memclr_amd64.s b/src/runtime/memclr_amd64.s
index 700bbd7b9b..26a6205e61 100644
--- a/src/runtime/memclr_amd64.s
+++ b/src/runtime/memclr_amd64.s
@@ -6,6 +6,7 @@
 
 #include "go_asm.h"
 #include "textflag.h"
+#include "asm_amd64.h"
 
 // See memclrNoHeapPointers Go doc for important implementation constraints.
 
@@ -39,6 +40,8 @@ tail:
 	JBE	_65through128
 	CMPQ	BX, $256
 	JBE	_129through256
+
+#ifndef hasAVX2
 	CMPB	internal∕cpu·X86+const_offsetX86HasAVX2(SB), $1
 	JE loop_preheader_avx2
 	// TODO: for really big clears, use MOVNTDQ, even without AVX2.
@@ -65,6 +68,7 @@ loop:
 	CMPQ	BX, $256
 	JAE	loop
 	JMP	tail
+#endif
 
 loop_preheader_avx2:
 	VPXOR Y0, Y0, Y0