diff --git a/src/cmd/8g/ggen.c b/src/cmd/8g/ggen.c
index 1095d5e441d..5570e128559 100644
--- a/src/cmd/8g/ggen.c
+++ b/src/cmd/8g/ggen.c
@@ -78,9 +78,9 @@ clearfat(Node *nl)
 	c = w % 4;	// bytes
 	q = w / 4;	// quads
 
-	gconreg(AMOVL, 0, D_AX);
 	nodreg(&n1, types[tptr], D_DI);
 	agen(nl, &n1);
+	gconreg(AMOVL, 0, D_AX);
 
 	if(q >= 4) {
 		gconreg(AMOVL, q, D_CX);
diff --git a/test/fixedbugs/issue5820.go b/test/fixedbugs/issue5820.go
new file mode 100644
index 00000000000..94de06d57db
--- /dev/null
+++ b/test/fixedbugs/issue5820.go
@@ -0,0 +1,18 @@
+// run
+
+// Copyright 2013 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.
+
+// issue 5820: register clobber when clearfat and 64 bit arithmetic is interleaved.
+
+package main
+
+func main() {
+	array := make([][]int, 2)
+	index := uint64(1)
+	array[index] = nil
+	if array[1] != nil {
+		panic("array[1] != nil")
+	}
+}