diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 18ecbff3cc..803acaa88d 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -789,18 +789,25 @@ var bodyReader = map[*ir.Func]pkgReaderIndex{}
 // constructed.
 var todoBodies []*ir.Func
 
-func (r *reader) addBody(fn *ir.Func) {
-	r.sync(syncAddBody)
+// Keep in sync with writer.implicitTypes
+// Also see comment there for why r.implicits and r.explicits should
+// never both be non-empty.
+func (r *reader) implicitTypes() []*types.Type {
+	r.sync(syncImplicitTypes)
 
-	// See commont in writer.addBody for why r.implicits and r.explicits
-	// should never both be non-empty.
 	implicits := r.implicits
 	if len(implicits) == 0 {
 		implicits = r.explicits
 	} else {
 		assert(len(r.explicits) == 0)
 	}
+	return implicits
+}
 
+func (r *reader) addBody(fn *ir.Func) {
+	r.sync(syncAddBody)
+
+	implicits := r.implicitTypes()
 	pri := pkgReaderIndex{r.p, r.reloc(relocBody), implicits}
 	bodyReader[fn] = pri
 
diff --git a/src/cmd/compile/internal/noder/sync.go b/src/cmd/compile/internal/noder/sync.go
index d77a784479..7326a6edbe 100644
--- a/src/cmd/compile/internal/noder/sync.go
+++ b/src/cmd/compile/internal/noder/sync.go
@@ -151,4 +151,5 @@ const (
 	syncLocalIdent
 	syncTypeParamNames
 	syncTypeParamBounds
+	syncImplicitTypes
 )
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index b39dd8651b..1475540d84 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -665,7 +665,9 @@ func (w *writer) pragmaFlag(p ir.PragmaFlag) {
 
 // @@@ Function bodies
 
-func (w *writer) addBody(sig *types2.Signature, block *syntax.BlockStmt, localsIdx map[types2.Object]int) {
+func (w *writer) implicitTypes() map[*types2.TypeParam]int {
+	w.sync(syncImplicitTypes)
+
 	// TODO(mdempsky): Theoretically, I think at this point we want to
 	// extend the implicit type parameters list with any new explicit
 	// type parameters.
@@ -684,9 +686,14 @@ func (w *writer) addBody(sig *types2.Signature, block *syntax.BlockStmt, localsI
 	} else {
 		assert(len(w.explicitIdx) == 0)
 	}
+	return implicitIdx
+}
 
+func (w *writer) addBody(sig *types2.Signature, block *syntax.BlockStmt, localsIdx map[types2.Object]int) {
 	w.sync(syncAddBody)
-	w.reloc(relocBody, w.p.bodyIdx(w.p.curpkg, sig, block, implicitIdx, localsIdx))
+
+	implicits := w.implicitTypes()
+	w.reloc(relocBody, w.p.bodyIdx(w.p.curpkg, sig, block, implicits, localsIdx))
 }
 
 func (pw *pkgWriter) bodyIdx(pkg *types2.Package, sig *types2.Signature, block *syntax.BlockStmt, implicitIdx map[*types2.TypeParam]int, localsIdx map[types2.Object]int) int {