diff --git a/wrap.go b/wrap.go
index 3e71058..a33459d 100644
--- a/wrap.go
+++ b/wrap.go
@@ -71,7 +71,7 @@
 // points, and if so, sets the target to its value and returns true. An error
 // matches a type if it is assignable to the target type, or if it has a method
 // As(interface{}) bool such that As(target) returns true. As will panic if target
-// is nil or not a pointer.
+// is not a non-nil pointer to a type which implements error or is of interface type.
 //
 // The As method should set the target to its value and return true if err
 // matches the type to which target points.
@@ -84,6 +84,9 @@
 	if typ.Kind() != reflect.Ptr || val.IsNil() {
 		panic("errors: target must be a non-nil pointer")
 	}
+	if e := typ.Elem(); e.Kind() != reflect.Interface && !e.Implements(errorType) {
+		panic("errors: *target must be interface or implement error")
+	}
 	targetType := typ.Elem()
 	for {
 		if reflect.TypeOf(err).AssignableTo(targetType) {
@@ -98,3 +101,5 @@
 		}
 	}
 }
+
+var errorType = reflect.TypeOf((*error)(nil)).Elem()
diff --git a/wrap_test.go b/wrap_test.go
index ef6a9ed..d08c325 100644
--- a/wrap_test.go
+++ b/wrap_test.go
@@ -151,10 +151,12 @@
 }
 
 func TestAsValidation(t *testing.T) {
+	var s string
 	testCases := []interface{}{
 		nil,
 		(*int)(nil),
 		"error",
+		&s,
 	}
 	err := xerrors.New("error")
 	for _, tc := range testCases {