diff --git a/config/interpolate.go b/config/interpolate.go
index a12fd11d5..bb526bf6a 100644
--- a/config/interpolate.go
+++ b/config/interpolate.go
@@ -282,6 +282,10 @@ func NewUserVariable(key string) (*UserVariable, error) {
 		name = name[:idx]
 	}
 
+	if len(elem) > 0 {
+		return nil, fmt.Errorf("Invalid dot index found: 'var.%s.%s'. Values in maps and lists can be referenced using square bracket indexing, like: 'var.mymap[\"key\"]' or 'var.mylist[1]'.", name, elem)
+	}
+
 	return &UserVariable{
 		key: key,
 
diff --git a/config/interpolate_test.go b/config/interpolate_test.go
index dc9d16b05..ac28ad0fb 100644
--- a/config/interpolate_test.go
+++ b/config/interpolate_test.go
@@ -2,6 +2,7 @@ package config
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/hil"
@@ -143,20 +144,10 @@ func TestNewUserVariable(t *testing.T) {
 	}
 }
 
-func TestNewUserVariable_map(t *testing.T) {
-	v, err := NewUserVariable("var.bar.baz")
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-
-	if v.Name != "bar" {
-		t.Fatalf("bad: %#v", v.Name)
-	}
-	if v.Elem != "baz" {
-		t.Fatalf("bad: %#v", v.Elem)
-	}
-	if v.FullKey() != "var.bar.baz" {
-		t.Fatalf("bad: %#v", v)
+func TestNewUserVariable_oldMapDotIndexErr(t *testing.T) {
+	_, err := NewUserVariable("var.bar.baz")
+	if err == nil || !strings.Contains(err.Error(), "Invalid dot index") {
+		t.Fatalf("Expected dot index err, got: %#v", err)
 	}
 }
 
diff --git a/config/test-fixtures/validate-good/main.tf b/config/test-fixtures/validate-good/main.tf
index 4af1f8dd6..89e14bfbe 100644
--- a/config/test-fixtures/validate-good/main.tf
+++ b/config/test-fixtures/validate-good/main.tf
@@ -22,7 +22,7 @@ resource "aws_security_group" "firewall" {
 }
 
 resource aws_instance "web" {
-    ami = "${var.amis.east}"
+    ami = "${var.amis["east"]}"
     security_groups = [
         "foo",
         "${aws_security_group.firewall.foo}"