diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 9ec6f8286e..6c1110a294 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1772,10 +1772,22 @@ func walkCall(n *Node, init *Nodes) {
 	var tempAssigns []*Node
 	for i, arg := range args {
 		updateHasCall(arg)
-		if instrumenting || arg.HasCall() {
+		// Determine param type.
+		var t *types.Type
+		if n.Op == OCALLMETH {
+			if i == 0 {
+				t = n.Left.Type.Recv().Type
+			} else {
+				t = params.Field(i - 1).Type
+			}
+		} else {
+			t = params.Field(i).Type
+		}
+		if instrumenting || fncall(arg, t) {
 			// make assignment of fncall to tempname
-			tmp := temp(arg.Type)
+			tmp := temp(t)
 			a := nod(OAS, tmp, arg)
+			a = convas(a, init)
 			tempAssigns = append(tempAssigns, a)
 			// replace arg with temp
 			args[i] = tmp
diff --git a/test/fixedbugs/issue28390.go b/test/fixedbugs/issue28390.go
new file mode 100644
index 0000000000..0a4d873182
--- /dev/null
+++ b/test/fixedbugs/issue28390.go
@@ -0,0 +1,39 @@
+// run
+
+// Copyright 2018 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 28390/28430: Function call arguments were not
+// converted correctly under some circumstances.
+
+package main
+
+import "fmt"
+
+type A struct {
+	K int
+	S string
+	M map[string]string
+}
+
+func newA(k int, s string) (a A) {
+	a.K = k
+	a.S = s
+	a.M = make(map[string]string)
+	a.M[s] = s
+	return
+}
+
+func proxy() (x int, a A) {
+	return 1, newA(2, "3")
+}
+
+func consume(x int, a interface{}) {
+	fmt.Println(x)
+	fmt.Println(a) // used to panic here
+}
+
+func main() {
+	consume(proxy())
+}
diff --git a/test/fixedbugs/issue28390.out b/test/fixedbugs/issue28390.out
new file mode 100644
index 0000000000..c923108f81
--- /dev/null
+++ b/test/fixedbugs/issue28390.out
@@ -0,0 +1,2 @@
+1
+{2 3 map[3:3]}
diff --git a/test/fixedbugs/issue28430.go b/test/fixedbugs/issue28430.go
new file mode 100644
index 0000000000..b59259abdc
--- /dev/null
+++ b/test/fixedbugs/issue28430.go
@@ -0,0 +1,17 @@
+// compile
+
+// Copyright 2018 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 28390/28430: Function call arguments were not
+// converted correctly under some circumstances.
+
+package main
+
+func g(_ interface{}, e error)
+func h() (int, error)
+
+func f() {
+	g(h())
+}