diff --git a/config/interpolate_funcs.go b/config/interpolate_funcs.go
index 03bf070b2..fbbe441ed 100644
--- a/config/interpolate_funcs.go
+++ b/config/interpolate_funcs.go
@@ -54,7 +54,7 @@ func interpolationFuncConcat() ast.Function {
 					continue
 				}
 
-				if strings.Contains(argument, InterpSplitDelim) {
+				if IsStringList(argument) {
 					isDeprecated = false
 				}
 
@@ -68,7 +68,7 @@ func interpolationFuncConcat() ast.Function {
 				return b.String(), nil
 			}
 
-			return strings.Join(finalList, InterpSplitDelim), nil
+			return NewStringList(finalList).String(), nil
 		},
 	}
 }
diff --git a/config/interpolate_funcs_test.go b/config/interpolate_funcs_test.go
index 488aed91c..dc6c93339 100644
--- a/config/interpolate_funcs_test.go
+++ b/config/interpolate_funcs_test.go
@@ -5,7 +5,6 @@ import (
 	"io/ioutil"
 	"os"
 	"reflect"
-	"strings"
 	"testing"
 
 	"github.com/hashicorp/terraform/config/lang"
@@ -42,74 +41,46 @@ func TestInterpolateFuncConcat(t *testing.T) {
 			// String + list
 			{
 				`${concat("a", split(",", "b,c"))}`,
-				fmt.Sprintf(
-					"%s%s%s%s%s",
-					"a",
-					InterpSplitDelim,
-					"b",
-					InterpSplitDelim,
-					"c"),
+				NewStringList([]string{"a", "b", "c"}).String(),
 				false,
 			},
 
 			// List + string
 			{
 				`${concat(split(",", "a,b"), "c")}`,
-				fmt.Sprintf(
-					"%s%s%s%s%s",
-					"a",
-					InterpSplitDelim,
-					"b",
-					InterpSplitDelim,
-					"c"),
+				NewStringList([]string{"a", "b", "c"}).String(),
 				false,
 			},
 
 			// Single list
 			{
 				`${concat(split(",", ",foo,"))}`,
-				fmt.Sprintf(
-					"%s%s%s",
-					InterpSplitDelim,
-					"foo",
-					InterpSplitDelim),
+				NewStringList([]string{"", "foo", ""}).String(),
 				false,
 			},
 			{
 				`${concat(split(",", "a,b,c"))}`,
-				fmt.Sprintf(
-					"%s%s%s%s%s",
-					"a",
-					InterpSplitDelim,
-					"b",
-					InterpSplitDelim,
-					"c"),
+				NewStringList([]string{"a", "b", "c"}).String(),
 				false,
 			},
 
 			// Two lists
 			{
 				`${concat(split(",", "a,b,c"), split(",", "d,e"))}`,
-				strings.Join([]string{
-					"a", "b", "c", "d", "e",
-				}, InterpSplitDelim),
+				NewStringList([]string{"a", "b", "c", "d", "e"}).String(),
 				false,
 			},
 			// Two lists with different separators
 			{
 				`${concat(split(",", "a,b,c"), split(" ", "d e"))}`,
-				strings.Join([]string{
-					"a", "b", "c", "d", "e",
-				}, InterpSplitDelim),
+				NewStringList([]string{"a", "b", "c", "d", "e"}).String(),
 				false,
 			},
 
 			// More lists
 			{
 				`${concat(split(",", "a,b"), split(",", "c,d"), split(",", "e,f"), split(",", "0,1"))}`,
-				strings.Join([]string{
-					"a", "b", "c", "d", "e", "f", "0", "1",
-				}, InterpSplitDelim),
+				NewStringList([]string{"a", "b", "c", "d", "e", "f", "0", "1"}).String(),
 				false,
 			},
 		},
@@ -204,7 +175,7 @@ func TestInterpolateFuncFormatList(t *testing.T) {
 			// formatlist applies to each list element in turn
 			{
 				`${formatlist("<%s>", split(",", "A,B"))}`,
-				"<A>" + StringListDelim + "<B>",
+				NewStringList([]string{"<A>", "<B>"}).String(),
 				false,
 			},
 			// formatlist repeats scalar elements
@@ -266,10 +237,7 @@ func TestInterpolateFuncJoin(t *testing.T) {
 
 			{
 				fmt.Sprintf(`${join(".", "%s")}`,
-					fmt.Sprintf(
-						"foo%sbar%sbaz",
-						StringListDelim,
-						StringListDelim)),
+					NewStringList([]string{"foo", "bar", "baz"}).String()),
 				"foo.bar.baz",
 				false,
 			},
@@ -394,39 +362,25 @@ func TestInterpolateFuncSplit(t *testing.T) {
 
 			{
 				`${split(",", ",,,")}`,
-				fmt.Sprintf(
-					"%s%s%s",
-					StringListDelim,
-					StringListDelim,
-					StringListDelim),
+				NewStringList([]string{"", "", "", ""}).String(),
 				false,
 			},
 
 			{
 				`${split(",", "foo,")}`,
-				fmt.Sprintf(
-					"%s%s",
-					"foo",
-					StringListDelim),
+				NewStringList([]string{"foo", ""}).String(),
 				false,
 			},
 
 			{
 				`${split(",", ",foo,")}`,
-				fmt.Sprintf(
-					"%s%s%s",
-					StringListDelim,
-					"foo",
-					StringListDelim),
+				NewStringList([]string{"", "foo", ""}).String(),
 				false,
 			},
 
 			{
 				`${split(".", "foo.bar.baz")}`,
-				fmt.Sprintf(
-					"foo%sbar%sbaz",
-					StringListDelim,
-					StringListDelim),
+				NewStringList([]string{"foo", "bar", "baz"}).String(),
 				false,
 			},
 		},
@@ -484,9 +438,7 @@ func TestInterpolateFuncKeys(t *testing.T) {
 		Cases: []testFunctionCase{
 			{
 				`${keys("foo")}`,
-				fmt.Sprintf(
-					"bar%squx",
-					StringListDelim),
+				NewStringList([]string{"bar", "qux"}).String(),
 				false,
 			},
 
@@ -533,9 +485,7 @@ func TestInterpolateFuncValues(t *testing.T) {
 		Cases: []testFunctionCase{
 			{
 				`${values("foo")}`,
-				fmt.Sprintf(
-					"quack%sbaz",
-					StringListDelim),
+				NewStringList([]string{"quack", "baz"}).String(),
 				false,
 			},
 
@@ -568,7 +518,7 @@ func TestInterpolateFuncElement(t *testing.T) {
 		Cases: []testFunctionCase{
 			{
 				fmt.Sprintf(`${element("%s", "1")}`,
-					"foo"+StringListDelim+"baz"),
+					NewStringList([]string{"foo", "baz"}).String()),
 				"baz",
 				false,
 			},
@@ -582,7 +532,7 @@ func TestInterpolateFuncElement(t *testing.T) {
 			// Invalid index should wrap vs. out-of-bounds
 			{
 				fmt.Sprintf(`${element("%s", "2")}`,
-					"foo"+StringListDelim+"baz"),
+					NewStringList([]string{"foo", "baz"}).String()),
 				"foo",
 				false,
 			},
@@ -590,7 +540,7 @@ func TestInterpolateFuncElement(t *testing.T) {
 			// Too many args
 			{
 				fmt.Sprintf(`${element("%s", "0", "2")}`,
-					"foo"+StringListDelim+"baz"),
+					NewStringList([]string{"foo", "baz"}).String()),
 				nil,
 				true,
 			},
diff --git a/config/interpolate_walk_test.go b/config/interpolate_walk_test.go
index 5155001e0..bc17dbddd 100644
--- a/config/interpolate_walk_test.go
+++ b/config/interpolate_walk_test.go
@@ -157,7 +157,7 @@ func TestInterpolationWalker_replace(t *testing.T) {
 					"bing",
 				},
 			},
-			Value: "bar" + StringListDelim + "baz",
+			Value: NewStringList([]string{"bar", "baz"}).String(),
 		},
 
 		{
@@ -168,7 +168,7 @@ func TestInterpolationWalker_replace(t *testing.T) {
 				},
 			},
 			Output: map[string]interface{}{},
-			Value:  UnknownVariableValue + StringListDelim + "baz",
+			Value:  NewStringList([]string{UnknownVariableValue, "baz"}).String(),
 		},
 	}
 
diff --git a/helper/schema/schema_test.go b/helper/schema/schema_test.go
index 2f7c259a5..bf5a3a19b 100644
--- a/helper/schema/schema_test.go
+++ b/helper/schema/schema_test.go
@@ -582,7 +582,7 @@ func TestSchemaMap_Diff(t *testing.T) {
 			},
 
 			ConfigVariables: map[string]string{
-				"var.foo": "2" + config.StringListDelim + "5",
+				"var.foo": config.NewStringList([]string{"2", "5"}).String(),
 			},
 
 			Diff: &terraform.InstanceDiff{
@@ -626,8 +626,8 @@ func TestSchemaMap_Diff(t *testing.T) {
 			},
 
 			ConfigVariables: map[string]string{
-				"var.foo": config.UnknownVariableValue +
-					config.StringListDelim + "5",
+				"var.foo": config.NewStringList([]string{
+					config.UnknownVariableValue, "5"}).String(),
 			},
 
 			Diff: &terraform.InstanceDiff{
@@ -905,7 +905,7 @@ func TestSchemaMap_Diff(t *testing.T) {
 			},
 
 			ConfigVariables: map[string]string{
-				"var.foo": "2" + config.StringListDelim + "5",
+				"var.foo": config.NewStringList([]string{"2", "5"}).String(),
 			},
 
 			Diff: &terraform.InstanceDiff{
@@ -952,8 +952,8 @@ func TestSchemaMap_Diff(t *testing.T) {
 			},
 
 			ConfigVariables: map[string]string{
-				"var.foo": config.UnknownVariableValue +
-					config.StringListDelim + "5",
+				"var.foo": config.NewStringList([]string{
+					config.UnknownVariableValue, "5"}).String(),
 			},
 
 			Diff: &terraform.InstanceDiff{