diff --git a/terraform/shadow_resource_provider.go b/terraform/shadow_resource_provider.go
index 84dc349be..d5ab83afc 100644
--- a/terraform/shadow_resource_provider.go
+++ b/terraform/shadow_resource_provider.go
@@ -48,6 +48,9 @@ func newShadowResourceProvider(p ResourceProvider) (ResourceProvider, shadowReso
 	// Create the shadow that watches the real value
 	shadow := &shadowResourceProviderShadow{
 		Shared: &shared,
+
+		resources:   p.Resources(),
+		dataSources: p.DataSources(),
 	}
 
 	return real, shadow
@@ -62,18 +65,6 @@ type shadowResourceProviderReal struct {
 	Shared *shadowResourceProviderShared
 }
 
-func (p *shadowResourceProviderReal) Resources() []ResourceType {
-	result := p.ResourceProvider.Resources()
-	p.Shared.Resources.SetValue(result)
-	return result
-}
-
-func (p *shadowResourceProviderReal) DataSources() []DataSource {
-	result := p.ResourceProvider.DataSources()
-	p.Shared.DataSources.SetValue(result)
-	return result
-}
-
 func (p *shadowResourceProviderReal) Close() error {
 	var result error
 	if c, ok := p.ResourceProvider.(ResourceProviderCloser); ok {
@@ -88,8 +79,8 @@ func (p *shadowResourceProviderReal) Input(
 	input UIInput, c *ResourceConfig) (*ResourceConfig, error) {
 	result, err := p.ResourceProvider.Input(input, c)
 	p.Shared.Input.SetValue(&shadowResourceProviderInput{
-		Config:    c,
-		Result:    result,
+		Config:    c.DeepCopy(),
+		Result:    result.DeepCopy(),
 		ResultErr: err,
 	})
 
@@ -102,35 +93,32 @@ func (p *shadowResourceProviderReal) Input(
 type shadowResourceProviderShadow struct {
 	Shared *shadowResourceProviderShared
 
+	// Cached values that are expected to not change
+	resources   []ResourceType
+	dataSources []DataSource
+
 	Error     error // Error is the list of errors from the shadow
 	ErrorLock sync.Mutex
 }
 
 type shadowResourceProviderShared struct {
-	CloseErr    shadow.Value
-	Input       shadow.Value
-	Resources   shadow.Value
-	DataSources shadow.Value
+	CloseErr shadow.Value
+	Input    shadow.Value
 }
 
-func (p *shadowResourceProviderShadow) CloseShadow() error { return nil }
+func (p *shadowResourceProviderShadow) CloseShadow() error {
+	// For now, just return the error. What we need to do in the future
+	// is marked the provider as "closed" so that any subsequent calls
+	// will fail out.
+	return p.Error
+}
 
 func (p *shadowResourceProviderShadow) Resources() []ResourceType {
-	v := p.Shared.Resources.Value()
-	if v == nil {
-		return nil
-	}
-
-	return v.([]ResourceType)
+	return p.resources
 }
 
 func (p *shadowResourceProviderShadow) DataSources() []DataSource {
-	v := p.Shared.DataSources.Value()
-	if v == nil {
-		return nil
-	}
-
-	return v.([]DataSource)
+	return p.dataSources
 }
 
 func (p *shadowResourceProviderShadow) Close() error {
diff --git a/terraform/shadow_resource_provider_test.go b/terraform/shadow_resource_provider_test.go
new file mode 100644
index 000000000..2acb4181c
--- /dev/null
+++ b/terraform/shadow_resource_provider_test.go
@@ -0,0 +1,115 @@
+package terraform
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+func TestShadowResourceProvider_cachedValues(t *testing.T) {
+	mock := new(MockResourceProvider)
+	real, shadow := newShadowResourceProvider(mock)
+
+	// Resources
+	{
+		actual := shadow.Resources()
+		expected := real.Resources()
+		if !reflect.DeepEqual(actual, expected) {
+			t.Fatalf("bad:\n\n%#v\n\n%#v", actual, expected)
+		}
+	}
+
+	// DataSources
+	{
+		actual := shadow.DataSources()
+		expected := real.DataSources()
+		if !reflect.DeepEqual(actual, expected) {
+			t.Fatalf("bad:\n\n%#v\n\n%#v", actual, expected)
+		}
+	}
+}
+
+func TestShadowResourceProviderInput(t *testing.T) {
+	mock := new(MockResourceProvider)
+	real, shadow := newShadowResourceProvider(mock)
+
+	// Test values
+	ui := new(MockUIInput)
+	config := testResourceConfig(t, map[string]interface{}{
+		"foo": "bar",
+	})
+	returnConfig := testResourceConfig(t, map[string]interface{}{
+		"bar": "baz",
+	})
+
+	// Configure the mock
+	mock.InputReturnConfig = returnConfig
+
+	// Verify that it blocks until the real input is called
+	var actual *ResourceConfig
+	var err error
+	doneCh := make(chan struct{})
+	go func() {
+		defer close(doneCh)
+		actual, err = shadow.Input(ui, config)
+	}()
+
+	select {
+	case <-doneCh:
+		t.Fatal("should block until finished")
+	case <-time.After(10 * time.Millisecond):
+	}
+
+	// Call the real input
+	realResult, realErr := real.Input(ui, config)
+	if !realResult.Equal(returnConfig) {
+		t.Fatalf("bad: %#v", realResult)
+	}
+	if realErr != nil {
+		t.Fatalf("bad: %s", realErr)
+	}
+
+	// The shadow should finish now
+	<-doneCh
+
+	// Verify the shadow returned the same values
+	if !actual.Equal(returnConfig) {
+		t.Fatalf("bad: %#v", actual)
+	}
+	if err != nil {
+		t.Fatalf("bad: %s", err)
+	}
+
+	// Verify we have no errors
+	if err := shadow.CloseShadow(); err != nil {
+		t.Fatalf("bad: %s", err)
+	}
+}
+
+func TestShadowResourceProviderInput_badInput(t *testing.T) {
+	mock := new(MockResourceProvider)
+	real, shadow := newShadowResourceProvider(mock)
+
+	// Test values
+	ui := new(MockUIInput)
+	config := testResourceConfig(t, map[string]interface{}{
+		"foo": "bar",
+	})
+	configBad := testResourceConfig(t, map[string]interface{}{
+		"foo": "nope",
+	})
+
+	// Call the real with one
+	real.Input(ui, config)
+
+	// Call the shadow with another
+	_, err := shadow.Input(ui, configBad)
+	if err != nil {
+		t.Fatalf("bad: %s", err)
+	}
+
+	// Verify we have an error
+	if err := shadow.CloseShadow(); err == nil {
+		t.Fatal("should have error")
+	}
+}