diff --git a/runtime/internal/lib/reflect/value.go b/runtime/internal/lib/reflect/value.go
index 9204f093..4e63cdfd 100644
--- a/runtime/internal/lib/reflect/value.go
+++ b/runtime/internal/lib/reflect/value.go
@@ -2609,7 +2609,7 @@ func methodReceiver(op string, v Value, methodIndex int) (rcvrtype *abi.Type, t
 			panic("reflect: " + op + " of method on nil interface value")
 		}
 		rcvrtype = iface.itab.typ
-		fn = unsafe.Pointer(&iface.itab.fun[i])
+		fn = unsafe.Pointer(iface.itab.fun[i])
 		t = (*funcType)(unsafe.Pointer(m.Typ_))
 	} else {
 		rcvrtype = v.typ()
@@ -3058,6 +3058,5 @@ func MakeMapWithSize(typ Type, n int) Value {
 	return Value{t, m, flag(Map)}
 }
 
-func ifaceE2I(t *abi.Type, src any, dst unsafe.Pointer) {
-	panic("todo: reflect.ifaceE2I")
-}
+//go:linkname ifaceE2I github.com/goplus/llgo/runtime/internal/runtime.IfaceE2I
+func ifaceE2I(t *abi.Type, src any, dst unsafe.Pointer)
diff --git a/runtime/internal/runtime/errors.go b/runtime/internal/runtime/errors.go
index 68790dd5..1516b7ad 100644
--- a/runtime/internal/runtime/errors.go
+++ b/runtime/internal/runtime/errors.go
@@ -4,6 +4,12 @@
 
 package runtime
 
+import (
+	"unsafe"
+
+	"github.com/goplus/llgo/runtime/abi"
+)
+
 // A boundsError represents an indexing or slicing operation gone wrong.
 type boundsError struct {
 	x int64
@@ -114,3 +120,54 @@ func itoa(buf []byte, val uint64) []byte {
 func PanicSliceConvert(x int, y int) {
 	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsConvert})
 }
+
+// A TypeAssertionError explains a failed type assertion.
+type TypeAssertionError struct {
+	_interface    *_type
+	concrete      *_type
+	asserted      *_type
+	missingMethod string // one method needed by Interface, missing from Concrete
+}
+
+func (*TypeAssertionError) RuntimeError() {}
+
+func (e *TypeAssertionError) Error() string {
+	inter := "interface"
+	if e._interface != nil {
+		inter = e._interface.String()
+	}
+	as := e.asserted.String()
+	if e.concrete == nil {
+		return "interface conversion: " + inter + " is nil, not " + as
+	}
+	cs := e.concrete.String()
+	if e.missingMethod == "" {
+		msg := "interface conversion: " + inter + " is " + cs + ", not " + as
+		if cs == as {
+			// provide slightly clearer error message
+			if pkgpath(e.concrete) != pkgpath(e.asserted) {
+				msg += " (types from different packages)"
+			} else {
+				msg += " (types from different scopes)"
+			}
+		}
+		return msg
+	}
+	return "interface conversion: " + cs + " is not " + as +
+		": missing method " + e.missingMethod
+}
+
+func pkgpath(t *_type) string {
+	if u := t.Uncommon(); u != nil {
+		return u.PkgPath_
+	}
+	switch t.Kind() {
+	case abi.Struct:
+		st := (*structtype)(unsafe.Pointer(t))
+		return st.PkgPath_
+	case abi.Interface:
+		it := (*interfacetype)(unsafe.Pointer(t))
+		return it.PkgPath_
+	}
+	return ""
+}
diff --git a/runtime/internal/runtime/z_face.go b/runtime/internal/runtime/z_face.go
index 6a9f37f2..7f1c61c0 100644
--- a/runtime/internal/runtime/z_face.go
+++ b/runtime/internal/runtime/z_face.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/goplus/llgo/runtime/abi"
 	c "github.com/goplus/llgo/runtime/internal/clite"
+	"github.com/goplus/llgo/runtime/internal/clite/pthread/sync"
 )
 
 type eface struct {
@@ -306,11 +307,50 @@ func Interface(pkgPath string, methods []Imethod) *InterfaceType {
 	return ret
 }
 
+var itabTable struct {
+	mutex
+	entries []*Itab
+}
+
+type mutex sync.Mutex
+
+func (m *mutex) Lock() {
+	if *(*c.Long)(unsafe.Pointer(m)) == 0 {
+		(*sync.Mutex)(m).Init(nil)
+	}
+	(*sync.Mutex)(m).Lock()
+}
+
+func (m *mutex) Unlock() {
+	(*sync.Mutex)(m).Unlock()
+}
+
+func findItab(inter *InterfaceType, typ *Type) *Itab {
+	itabTable.Lock()
+	for _, i := range itabTable.entries {
+		if i.inter == inter && i._type == typ {
+			itabTable.Unlock()
+			return i
+		}
+	}
+	itabTable.Unlock()
+	return nil
+}
+
+func addItab(i *Itab) {
+	itabTable.Lock()
+	itabTable.entries = append(itabTable.entries, i)
+	itabTable.Unlock()
+}
+
 // NewItab returns a new itab.
 func NewItab(inter *InterfaceType, typ *Type) *Itab {
 	if typ == nil {
 		return nil
 	}
+	if i := findItab(inter, typ); i != nil {
+		return i
+	}
 	n := len(inter.Methods)
 	size := itabHdrSize + uintptr(n)*pointerSize
 	ptr := AllocU(size)
@@ -335,6 +375,9 @@ func NewItab(inter *InterfaceType, typ *Type) *Itab {
 			*c.Advance(data, i) = uintptr(fn)
 		}
 	}
+	if ret.fun[0] != 0 {
+		addItab(ret)
+	}
 	return ret
 }
 
@@ -632,4 +675,41 @@ func shallowHashTuple(tuple []*Type) uint32 {
 	return hash
 }
 
+func assertE2I(inter *interfacetype, t *_type) *itab {
+	if t == nil {
+		// explicit conversions require non-nil interface value.
+		panic(&TypeAssertionError{nil, nil, &inter.Type, ""})
+	}
+	return getitab(inter, t, false)
+}
+
+func IfaceE2I(inter *interfacetype, e eface, dst *iface) {
+	*dst = iface{assertE2I(inter, e._type), e.data}
+}
+
+func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
+	if len(inter.Methods) == 0 {
+		panic("internal error - misuse of itab")
+	}
+
+	// easy case
+	if typ.TFlag&abi.TFlagUncommon == 0 {
+		if canfail {
+			return nil
+		}
+		name := inter.Methods[0].Name()
+		panic(&TypeAssertionError{nil, typ, &inter.Type, name})
+	}
+
+	m := NewItab(inter, typ)
+
+	if m.fun[0] != 0 {
+		return m
+	}
+	if canfail {
+		return nil
+	}
+	panic(&TypeAssertionError{concrete: typ, asserted: &inter.Type, missingMethod: ""})
+}
+
 // -----------------------------------------------------------------------------