diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 82d232f940..9746fbd316 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -3206,6 +3206,11 @@ func (s *state) exprCheckPtr(n ir.Node, checkPtrOK bool) *ssa.Value {
 		n := n.(*ir.BinaryExpr)
 		ptr := s.expr(n.X)
 		len := s.expr(n.Y)
+
+		// Force len to uintptr to prevent misuse of garbage bits in the
+		// upper part of the register (#48536).
+		len = s.conv(n, len, len.Type, types.Types[types.TUINTPTR])
+
 		return s.newValue2(ssa.OpAddPtr, n.Type(), ptr, len)
 
 	default:
diff --git a/test/fixedbugs/issue48536.go b/test/fixedbugs/issue48536.go
new file mode 100644
index 0000000000..68c7d1c261
--- /dev/null
+++ b/test/fixedbugs/issue48536.go
@@ -0,0 +1,29 @@
+// run
+
+// 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.
+
+package main
+
+import "unsafe"
+
+var i = 257
+
+func main() {
+	var buf [10]byte
+	p0 := unsafe.Pointer(&buf[0])
+	p1 := unsafe.Pointer(&buf[1])
+
+	if p := unsafe.Add(p0, uint8(i)); p != p1 {
+		println("FAIL:", p, "!=", p1)
+	}
+
+	var x uint8
+	if i != 0 {
+		x = 1
+	}
+	if p := unsafe.Add(p0, x); p != p1 {
+		println("FAIL:", p, "!=", p1)
+	}
+}