diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index d1097e8236..f0a913275a 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -89,6 +89,7 @@ var debugtab = []struct {
 	{"dwarfinl", "print information about DWARF inlined function creation", &Debug_gendwarfinl},
 	{"softfloat", "force compiler to emit soft-float code", &Debug_softfloat},
 	{"defer", "print information about defer compilation", &Debug_defer},
+	{"fieldtrack", "enable fieldtracking", &objabi.Fieldtrack_enabled},
 }
 
 const debugHelpHeader = `usage: -d arg[,arg]* and arg is <key>[=<value>]
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index cbba5ff79c..c0b05035f0 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -6,7 +6,6 @@ package gc
 
 import (
 	"cmd/compile/internal/types"
-	"cmd/internal/objabi"
 	"fmt"
 	"strings"
 )
@@ -2442,15 +2441,6 @@ func derefall(t *types.Type) *types.Type {
 	return t
 }
 
-type typeSymKey struct {
-	t *types.Type
-	s *types.Sym
-}
-
-// dotField maps (*types.Type, *types.Sym) pairs to the corresponding struct field (*types.Type with Etype==TFIELD).
-// It is a cache for use during usefield in walk.go, only enabled when field tracking.
-var dotField = map[typeSymKey]*types.Field{}
-
 func lookdot(n *Node, t *types.Type, dostrcmp int) *types.Field {
 	s := n.Sym
 
@@ -2481,9 +2471,6 @@ func lookdot(n *Node, t *types.Type, dostrcmp int) *types.Field {
 		}
 		n.Xoffset = f1.Offset
 		n.Type = f1.Type
-		if objabi.Fieldtrack_enabled > 0 {
-			dotField[typeSymKey{t.Orig, s}] = f1
-		}
 		if t.IsInterface() {
 			if n.Left.Type.IsPtr() {
 				n.Left = nod(ODEREF, n.Left, nil) // implicitstar
@@ -2492,6 +2479,8 @@ func lookdot(n *Node, t *types.Type, dostrcmp int) *types.Field {
 			}
 
 			n.Op = ODOTINTER
+		} else {
+			n.SetOpt(f1)
 		}
 
 		return f1
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 82898c8167..a7b6e7fcb3 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -3734,10 +3734,13 @@ func usefield(n *Node) {
 	if t.IsPtr() {
 		t = t.Elem()
 	}
-	field := dotField[typeSymKey{t.Orig, n.Sym}]
+	field := n.Opt().(*types.Field)
 	if field == nil {
 		Fatalf("usefield %v %v without paramfld", n.Left.Type, n.Sym)
 	}
+	if field.Sym != n.Sym || field.Offset != n.Xoffset {
+		Fatalf("field inconsistency: %v,%v != %v,%v", field.Sym, field.Offset, n.Sym, n.Xoffset)
+	}
 	if !strings.Contains(field.Note, "go:\"track\"") {
 		return
 	}
diff --git a/test/fixedbugs/issue42686.go b/test/fixedbugs/issue42686.go
new file mode 100644
index 0000000000..962bdd35cb
--- /dev/null
+++ b/test/fixedbugs/issue42686.go
@@ -0,0 +1,11 @@
+// compile -d=fieldtrack
+
+// Copyright 2020 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 p
+
+func a(x struct{ f int }) { _ = x.f }
+
+func b() { a(struct{ f int }{}) }