diff --git a/terraform/resource_provider.go b/terraform/resource_provider.go
index 613bb749b..d530561d1 100644
--- a/terraform/resource_provider.go
+++ b/terraform/resource_provider.go
@@ -1,10 +1,5 @@
 package terraform
 
-// ComputedPlaceholder is the placeholder value for computed attributes.
-// ResourceProviders can compare values to this during a diff to determine
-// if it is just a placeholder.
-const ComputedPlaceholder = "74D93920-ED26-11E3-AC10-0800200C9A66"
-
 // ResourceProvider is an interface that must be implemented by any
 // resource provider: the thing that creates and manages the resources in
 // a Terraform configuration.
diff --git a/terraform/state.go b/terraform/state.go
index e40e13b05..9ade06428 100644
--- a/terraform/state.go
+++ b/terraform/state.go
@@ -2,6 +2,8 @@ package terraform
 
 import (
 	"sync"
+
+	"github.com/hashicorp/terraform/config"
 )
 
 // State keeps track of a snapshot state-of-the-world that Terraform
@@ -43,8 +45,7 @@ type ResourceState struct {
 // won't be available until apply, the value is replaced with the
 // computeID.
 func (s *ResourceState) MergeDiff(
-	d map[string]*ResourceAttrDiff,
-	computedID string) *ResourceState {
+	d map[string]*ResourceAttrDiff) *ResourceState {
 	var result ResourceState
 	if s != nil {
 		result = *s
@@ -58,7 +59,7 @@ func (s *ResourceState) MergeDiff(
 	}
 	for k, diff := range d {
 		if diff.NewComputed {
-			result.Attributes[k] = computedID
+			result.Attributes[k] = config.UnknownVariableValue
 			continue
 		}
 
diff --git a/terraform/state_test.go b/terraform/state_test.go
index efb4369ca..44b8d3e4e 100644
--- a/terraform/state_test.go
+++ b/terraform/state_test.go
@@ -3,6 +3,8 @@ package terraform
 import (
 	"reflect"
 	"testing"
+
+	"github.com/hashicorp/terraform/config"
 )
 
 func TestResourceState_MergeDiff(t *testing.T) {
@@ -29,12 +31,12 @@ func TestResourceState_MergeDiff(t *testing.T) {
 		},
 	}
 
-	rs2 := rs.MergeDiff(diff, "what")
+	rs2 := rs.MergeDiff(diff)
 
 	expected := map[string]string{
 		"foo": "baz",
 		"bar": "foo",
-		"baz": "what",
+		"baz": config.UnknownVariableValue,
 	}
 
 	if !reflect.DeepEqual(expected, rs2.Attributes) {
@@ -52,7 +54,7 @@ func TestResourceState_MergeDiff_nil(t *testing.T) {
 		},
 	}
 
-	rs2 := rs.MergeDiff(diff, "computed")
+	rs2 := rs.MergeDiff(diff)
 
 	expected := map[string]string{
 		"foo": "baz",
diff --git a/terraform/terraform.go b/terraform/terraform.go
index c2fc131ed..519c7654a 100644
--- a/terraform/terraform.go
+++ b/terraform/terraform.go
@@ -144,11 +144,13 @@ func (t *Terraform) diffWalkFn(
 			rs = state.resources[r.Id()]
 		}
 		if len(vars) > 0 {
-			r = r.ReplaceVariables(vars)
+			if err := r.RawConfig.Interpolate(vars); err != nil {
+				panic(fmt.Sprintf("Interpolate error: %s", err))
+			}
 		}
 		l.RUnlock()
 
-		diff, err := p.Provider.Diff(rs, r.Config)
+		diff, err := p.Provider.Diff(rs, r.RawConfig.Config())
 		if err != nil {
 			return err
 		}
@@ -166,7 +168,7 @@ func (t *Terraform) diffWalkFn(
 		result.Resources[r.Id()] = diff
 
 		// Determine the new state and update variables
-		rs = rs.MergeDiff(diff.Attributes, ComputedPlaceholder)
+		rs = rs.MergeDiff(diff.Attributes)
 		for ak, av := range rs.Attributes {
 			vars[fmt.Sprintf("%s.%s", r.Id(), ak)] = av
 		}
@@ -179,7 +181,11 @@ func (t *terraformProvider) init(vars map[string]string) (err error) {
 	t.Once.Do(func() {
 		var c map[string]interface{}
 		if t.Config != nil {
-			c = t.Config.ReplaceVariables(vars).Config
+			if err := t.Config.RawConfig.Interpolate(vars); err != nil {
+				panic(err)
+			}
+
+			c = t.Config.RawConfig.Config()
 		}
 
 		err = t.Provider.Configure(c)
diff --git a/terraform/terraform_test.go b/terraform/terraform_test.go
index 9422f3f60..f703820fc 100644
--- a/terraform/terraform_test.go
+++ b/terraform/terraform_test.go
@@ -47,7 +47,7 @@ func TestNew(t *testing.T) {
 	}
 
 	pc = testProviderConfig(tf, "aws_instance.foo")
-	if pc.Config["foo"].(string) != "bar" {
+	if pc.RawConfig.Raw["foo"].(string) != "bar" {
 		t.Fatalf("bad: %#v", pc)
 	}
 }
@@ -114,11 +114,11 @@ func TestNew_providerConfigCache(t *testing.T) {
 		t.Fatalf("bad: %#v", pc)
 	}
 	pc = testProviderConfig(tf, "aws_instance.foo")
-	if pc.Config["foo"].(string) != "bar" {
+	if pc.RawConfig.Raw["foo"].(string) != "bar" {
 		t.Fatalf("bad: %#v", pc)
 	}
 	pc = testProviderConfig(tf, "aws_elb.lb")
-	if pc.Config["foo"].(string) != "baz" {
+	if pc.RawConfig.Raw["foo"].(string) != "baz" {
 		t.Fatalf("bad: %#v", pc)
 	}
 
@@ -299,7 +299,7 @@ func testProviderFunc(n string, rs []string) ResourceProviderFactory {
 					New: v.(string),
 				}
 
-				if strings.Contains(attrDiff.New, ComputedPlaceholder) {
+				if strings.Contains(attrDiff.New, config.UnknownVariableValue) {
 					attrDiff.NewComputed = true
 				}