diff --git a/env/env.go b/env/env.go
index d8faa70f..7af9dbb4 100644
--- a/env/env.go
+++ b/env/env.go
@@ -21,6 +21,8 @@ type (
 		parent         *Env
 		values         map[string]reflect.Value
 		types          map[string]reflect.Type
+		packages       map[string]map[string]reflect.Value
+		packageTypes   map[string]map[string]reflect.Type
 		externalLookup ExternalLookup
 	}
 )
diff --git a/env/envPackage.go b/env/envPackage.go
new file mode 100644
index 00000000..7bd48c16
--- /dev/null
+++ b/env/envPackage.go
@@ -0,0 +1,76 @@
+package env
+
+import "reflect"
+
+// Package returns the methods for the package defined by name.
+// If no package is found by this name in the environment,
+// the globally defined package with this name is returned.
+func (e *Env) Package(name string) map[string]reflect.Value {
+	e.rwMutex.RLock()
+	pkg, ok := e.packages[name]
+	e.rwMutex.RUnlock()
+
+	if ok {
+		return pkg
+	}
+
+	if e.parent == nil {
+		pkg, ok := Packages[name]
+		if ok {
+			return pkg
+		}
+	}
+
+	return nil
+}
+
+// DefinePackage defines methods for the package name.
+func (e *Env) DefinePackage(name string, values map[string]reflect.Value) {
+	e.rwMutex.RLock()
+	defer e.rwMutex.RUnlock()
+
+	if e.packages == nil {
+		e.packages = map[string]map[string]reflect.Value{}
+	}
+	e.packages[name] = make(map[string]reflect.Value, len(values))
+	for k, v := range values {
+		e.packages[name][k] = v
+	}
+}
+
+// PackageTypes returns the types for the package defined by name.
+// If no package is found by this name in the environment,
+// the globally defined package with this name is returned
+func (e *Env) PackageTypes(name string) map[string]reflect.Type {
+	e.rwMutex.RLock()
+	pkg, ok := e.packageTypes[name]
+	e.rwMutex.RUnlock()
+
+	if ok {
+		return pkg
+	}
+
+	if e.parent == nil {
+		pkg, ok := PackageTypes[name]
+		if ok {
+			return pkg
+		}
+	}
+
+	return nil
+}
+
+// DefinePackageTypes defines types for the package name.
+func (e *Env) DefinePackageTypes(name string, types map[string]reflect.Type) {
+	e.rwMutex.RLock()
+	defer e.rwMutex.RUnlock()
+
+	if e.packageTypes == nil {
+		e.packageTypes = map[string]map[string]reflect.Type{}
+	}
+
+	e.packageTypes[name] = make(map[string]reflect.Type, len(types))
+	for k, v := range types {
+		e.packageTypes[name][k] = v
+	}
+}
diff --git a/env/envPackage_test.go b/env/envPackage_test.go
new file mode 100644
index 00000000..383c046f
--- /dev/null
+++ b/env/envPackage_test.go
@@ -0,0 +1,92 @@
+package env
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestDefinePackage(t *testing.T) {
+	e := NewEnv()
+
+	if custom := e.Package("custom"); custom != nil {
+		t.Fatal("unexpected \"custom\" package", custom)
+	}
+
+	// Define the method "hello" for the package "custom" using the global variable.
+	Packages["custom"] = map[string]reflect.Value{
+		"hello": reflect.ValueOf(func() string { return "hello" }),
+	}
+
+	if custom := e.Package("custom"); custom == nil {
+		t.Fatal("expected \"custom\" package")
+	} else if hello, ok := custom["hello"]; !ok {
+		t.Fatal("expected method definition \"hello\" in package \"custom\"")
+	} else if fn, ok := hello.Interface().(func() string); !ok {
+		t.Fatal("expected method func() string {}")
+	} else if res := fn(); res != "hello" {
+		t.Fatalf("expected return value \"hello\" but got %v", res)
+	}
+
+	// Re-define the method for the package "custom" at the environment level.
+	e.DefinePackage("custom", map[string]reflect.Value{
+		"hello": reflect.ValueOf(func() string { return "hallo" }),
+	})
+
+	if custom := e.Package("custom"); custom == nil {
+		t.Fatal("expected \"custom\" package")
+	} else if hello, ok := custom["hello"]; !ok {
+		t.Fatal("expected method definition \"hello\" in package \"custom\"")
+	} else if fn, ok := hello.Interface().(func() string); !ok {
+		t.Fatal("expected method func() string {}")
+	} else if res := fn(); res != "hallo" {
+		t.Fatalf("expected return value \"hallo\" but got %v", res)
+	}
+}
+
+func TestDefinePackageTypes(t *testing.T) {
+	e := NewEnv()
+
+	if custom := e.PackageTypes("custom"); custom != nil {
+		t.Fatal("unexpected \"custom\" package", custom)
+	}
+
+	type A struct {
+		a string
+	}
+
+	// Define the type "A" for the package "custom" using the global variable.
+	PackageTypes["custom"] = map[string]reflect.Type{
+		"A": reflect.TypeOf(A{}),
+	}
+
+	if custom := e.PackageTypes("custom"); custom == nil {
+		t.Fatal("expected \"custom\" package")
+	} else if typeA, ok := custom["A"]; !ok {
+		t.Fatal("expected type definition \"A\" in package \"custom\"")
+	} else {
+		a := reflect.New(typeA).Interface()
+		if is, want := a, (&A{}); !reflect.DeepEqual(is, want) {
+			t.Fatalf("%T != %T", is, want)
+		}
+	}
+
+	type B struct {
+		b int
+	}
+
+	// Re-define the type for the package "custom" at the environment level.
+	e.DefinePackageTypes("custom", map[string]reflect.Type{
+		"A": reflect.TypeOf(B{}),
+	})
+
+	if custom := e.PackageTypes("custom"); custom == nil {
+		t.Fatal("expected \"custom\" package")
+	} else if typeA, ok := custom["A"]; !ok {
+		t.Fatal("expected type definition \"A\" in package \"custom\"")
+	} else {
+		a := reflect.New(typeA).Interface()
+		if is, want := a, (&B{}); !reflect.DeepEqual(is, want) {
+			t.Fatalf("%T != %T", is, want)
+		}
+	}
+}
diff --git a/vm/vmExpr.go b/vm/vmExpr.go
index bf8f1f39..a5d55ba2 100644
--- a/vm/vmExpr.go
+++ b/vm/vmExpr.go
@@ -522,8 +522,8 @@ func (runInfo *runInfoStruct) invokeExpr() {
 		name := runInfo.rv.String()
 		runInfo.rv = nilValue
 
-		methods, ok := env.Packages[name]
-		if !ok {
+		methods := runInfo.env.Package(name)
+		if methods == nil {
 			runInfo.err = newStringError(expr, "package not found: "+name)
 			return
 		}
@@ -537,8 +537,8 @@ func (runInfo *runInfoStruct) invokeExpr() {
 			}
 		}
 
-		types, ok := env.PackageTypes[name]
-		if ok {
+		types := runInfo.env.PackageTypes(name)
+		if types != nil {
 			for typeName, typeValue := range types {
 				err = pack.DefineReflectType(typeName, typeValue)
 				if err != nil {