diff --git a/builtin/providers/aws/resource_aws_elb.go b/builtin/providers/aws/resource_aws_elb.go
index 1b606fa19..d62f69552 100644
--- a/builtin/providers/aws/resource_aws_elb.go
+++ b/builtin/providers/aws/resource_aws_elb.go
@@ -104,12 +104,12 @@ func resource_aws_elb_update(
 		var toAdd []string
 
 		for _, instanceId := range mergedInstances {
-		   for _, prevId := range previousInstances {
+			for _, prevId := range previousInstances {
 				// If the merged instance ID existed
 				// previously, we don't have to do anything
 				if instanceId == prevId {
 					continue
-				// Otherwise, we need to add it to the load balancer
+					// Otherwise, we need to add it to the load balancer
 				} else {
 					toAdd = append(toAdd, instanceId)
 				}
@@ -117,14 +117,14 @@ func resource_aws_elb_update(
 		}
 
 		for i, instanceId := range toAdd {
-		   for _, prevId := range previousInstances {
+			for _, prevId := range previousInstances {
 				// If the instance ID we are adding existed
 				// previously, we want to not add it, but rather remove
 				// it
 				if instanceId == prevId {
 					toRemove = append(toRemove, instanceId)
 					toAdd = append(toAdd[:i], toAdd[i+1:]...)
-				// Otherwise, we continue adding it to the ELB
+					// Otherwise, we continue adding it to the ELB
 				} else {
 					continue
 				}
diff --git a/builtin/providers/aws/resource_aws_instance.go b/builtin/providers/aws/resource_aws_instance.go
index 173a032de..3d1f1c5c4 100644
--- a/builtin/providers/aws/resource_aws_instance.go
+++ b/builtin/providers/aws/resource_aws_instance.go
@@ -29,16 +29,8 @@ func resource_aws_instance_create(
 
 	// Figure out user data
 	userData := ""
-	if v, ok := rs.Attributes["user_data"]; ok {
-		userData = v
-		delete(rs.Attributes, "user_data")
-	}
-
-	if userData != "" {
-		// Set the SHA1 hash of the data as an attribute so we can
-		// compare for diffs.
-		hash := sha1.Sum([]byte(userData))
-		rs.Attributes["user_data_hash"] = hex.EncodeToString(hash[:])
+	if attr, ok := d.Attributes["user_data"]; ok {
+		userData = attr.NewExtra.(string)
 	}
 
 	// Build the creation struct
@@ -210,9 +202,15 @@ func resource_aws_instance_diff(
 			"security_groups",
 			"subnet_id",
 		},
-	}
 
-	// TODO(mitchellh): figure out way to diff user_data_hash
+		PreProcess: map[string]diff.PreProcessFunc{
+			"user_data": func(v string) string {
+				println("SUMMIN: " + v)
+				hash := sha1.Sum([]byte(v))
+				return hex.EncodeToString(hash[:])
+			},
+		},
+	}
 
 	return b.Diff(s, c)
 }
diff --git a/builtin/providers/aws/resource_aws_instance_test.go b/builtin/providers/aws/resource_aws_instance_test.go
index 5996da63d..3ce3bb241 100644
--- a/builtin/providers/aws/resource_aws_instance_test.go
+++ b/builtin/providers/aws/resource_aws_instance_test.go
@@ -36,7 +36,23 @@ func TestAccAWSInstance_normal(t *testing.T) {
 					testCheck,
 					resource.TestCheckResourceAttr(
 						"aws_instance.foo",
-						"user_data_hash",
+						"user_data",
+						"0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"),
+				),
+			},
+
+			// We repeat the exact same test so that we can be sure
+			// that the user data hash stuff is working without generating
+			// an incorrect diff.
+			resource.TestStep{
+				Config: testAccInstanceConfig,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckInstanceExists(
+						"aws_instance.foo", &v),
+					testCheck,
+					resource.TestCheckResourceAttr(
+						"aws_instance.foo",
+						"user_data",
 						"0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"),
 				),
 			},