diff --git a/_test/cli7.go b/_test/cli7.go
new file mode 100644
index 000000000..fbe2f19dc
--- /dev/null
+++ b/_test/cli7.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+)
+
+type T struct {
+	http.ResponseWriter
+}
+
+type mw1 struct {
+}
+
+var obj = map[string]interface{}{}
+
+func (m *mw1) ServeHTTP(rw http.ResponseWriter, rq *http.Request) {
+	t := &T{
+		ResponseWriter: rw,
+	}
+	x := t.Header()
+	i := obj["m1"].(*mw1)
+	fmt.Fprint(rw, "Welcome to my website!", x, i)
+}
+
+func main() {
+	m1 := &mw1{}
+
+	obj["m1"] = m1
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", m1.ServeHTTP)
+
+	server := httptest.NewServer(mux)
+	defer server.Close()
+
+	client(server.URL)
+}
+
+func client(uri string) {
+	resp, err := http.Get(uri)
+	if err != nil {
+		log.Fatal(err)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(string(body))
+}
+
+// Output:
+// Welcome to my website!map[] &{}
diff --git a/_test/type24.go b/_test/type24.go
index 79449d666..7bcb94ba3 100644
--- a/_test/type24.go
+++ b/_test/type24.go
@@ -43,6 +43,6 @@ func assertValue() {
 }
 
 // Output:
-// interface conversion: interface {} is int, not string
-// interface conversion: interface {} is nil, not string
-// interface conversion: *httptest.ResponseRecorder is not http.Pusher: missing method Push
+// 22:10: interface conversion: interface {} is int, not string
+// 32:10: interface conversion: interface {} is nil, not string
+// 42:10: interface conversion: *httptest.ResponseRecorder is not http.Pusher: missing method Push
diff --git a/interp/interp_consistent_test.go b/interp/interp_consistent_test.go
index 0187b215b..d1c430c88 100644
--- a/interp/interp_consistent_test.go
+++ b/interp/interp_consistent_test.go
@@ -109,6 +109,7 @@ func TestInterpConsistencyBuild(t *testing.T) {
 			file.Name() == "range9.go" || // expect error
 			file.Name() == "unsafe6.go" || // needs go.mod to be 1.17
 			file.Name() == "unsafe7.go" || // needs go.mod to be 1.17
+			file.Name() == "type24.go" || // expect error
 			file.Name() == "type27.go" || // expect error
 			file.Name() == "type28.go" || // expect error
 			file.Name() == "type29.go" || // expect error
diff --git a/interp/interp_file_test.go b/interp/interp_file_test.go
index f29b117df..d9f1e208f 100644
--- a/interp/interp_file_test.go
+++ b/interp/interp_file_test.go
@@ -7,6 +7,7 @@ import (
 	"go/token"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 
@@ -76,7 +77,9 @@ func runCheck(t *testing.T, p string) {
 		t.Fatal(err)
 	}
 
-	if res := strings.TrimSpace(stdout.String()); res != wanted {
+	// Remove path in output, to have results independent of location.
+	re := regexp.MustCompile(p + ":")
+	if res := re.ReplaceAllString(strings.TrimSpace(stdout.String()), ""); res != wanted {
 		t.Errorf("\ngot:  %q,\nwant: %q", res, wanted)
 	}
 }
diff --git a/interp/run.go b/interp/run.go
index 7660d1df0..c592b606d 100644
--- a/interp/run.go
+++ b/interp/run.go
@@ -401,7 +401,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			ok = v.IsValid()
 			if !ok {
 				if !withOk {
-					panic(fmt.Sprintf("interface conversion: interface {} is nil, not %s", rtype.String()))
+					panic(n.cfgErrorf("interface conversion: interface {} is nil, not %s", rtype.String()))
 				}
 				return next
 			}
@@ -409,7 +409,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			if !ok {
 				if !withOk {
 					method := firstMissingMethod(leftType, rtype)
-					panic(fmt.Sprintf("interface conversion: %s is not %s: missing method %s", leftType.String(), rtype.String(), method))
+					panic(n.cfgErrorf("interface conversion: %s is not %s: missing method %s", leftType.String(), rtype.String(), method))
 				}
 				return next
 			}
@@ -430,14 +430,18 @@ func typeAssert(n *node, withResult, withOk bool) {
 			concrete := val.Interface()
 			ctyp := reflect.TypeOf(concrete)
 
+			if vv, ok := concrete.(valueInterface); ok {
+				ctyp = vv.value.Type()
+				concrete = vv.value.Interface()
+			}
 			ok = canAssertTypes(ctyp, rtype)
 			if !ok {
 				if !withOk {
 					// TODO(mpl): think about whether this should ever happen.
 					if ctyp == nil {
-						panic(fmt.Sprintf("interface conversion: interface {} is nil, not %s", rtype.String()))
+						panic(n.cfgErrorf("interface conversion: interface {} is nil, not %s", rtype.String()))
 					}
-					panic(fmt.Sprintf("interface conversion: interface {} is %s, not %s", ctyp.String(), rtype.String()))
+					panic(n.cfgErrorf("interface conversion: interface {} is %s, not %s", ctyp.String(), rtype.String()))
 				}
 				return next
 			}
@@ -462,7 +466,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			}
 			if !ok {
 				if !withOk {
-					panic(fmt.Sprintf("interface conversion: interface {} is nil, not %s", rtype.String()))
+					panic(n.cfgErrorf("interface conversion: interface {} is nil, not %s", rtype.String()))
 				}
 				return next
 			}
@@ -475,7 +479,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			if !ok {
 				if !withOk {
 					method := firstMissingMethod(v.Type(), rtype)
-					panic(fmt.Sprintf("interface conversion: %s is not %s: missing method %s", v.Type().String(), rtype.String(), method))
+					panic(n.cfgErrorf("interface conversion: %s is not %s: missing method %s", v.Type().String(), rtype.String(), method))
 				}
 				return next
 			}
@@ -495,7 +499,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			if !ok || !v.value.IsValid() {
 				ok = false
 				if !withOk {
-					panic(fmt.Sprintf("interface conversion: interface {} is nil, not %s", rtype.String()))
+					panic(n.cfgErrorf("interface conversion: interface {} is nil, not %s", rtype.String()))
 				}
 				return next
 			}
@@ -503,7 +507,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 			ok = canAssertTypes(v.value.Type(), rtype)
 			if !ok {
 				if !withOk {
-					panic(fmt.Sprintf("interface conversion: interface {} is %s, not %s", v.value.Type().String(), rtype.String()))
+					panic(n.cfgErrorf("interface conversion: interface {} is %s, not %s", v.value.Type().String(), rtype.String()))
 				}
 				return next
 			}
@@ -567,7 +571,7 @@ func convert(n *node) {
 		n.exec = func(f *frame) bltn {
 			n, ok := value(f).Interface().(*node)
 			if !ok || !n.typ.convertibleTo(c.typ) {
-				panic("cannot convert")
+				panic(n.cfgErrorf("cannot convert to %s", c.typ.id()))
 			}
 			n1 := *n
 			n1.typ = c.typ
@@ -3611,7 +3615,7 @@ func convertConstantValue(n *node) {
 	case constant.Int:
 		i, x := constant.Int64Val(c)
 		if !x {
-			panic(fmt.Sprintf("constant %s overflows int64", c.ExactString()))
+			panic(n.cfgErrorf("constant %s overflows int64", c.ExactString()))
 		}
 		v = reflect.ValueOf(int(i))
 	case constant.Float: