diff --git a/builtin/providers/azurerm/resource_arm_virtual_machine.go b/builtin/providers/azurerm/resource_arm_virtual_machine.go
index 2f1fbce771..7cc1d19b39 100644
--- a/builtin/providers/azurerm/resource_arm_virtual_machine.go
+++ b/builtin/providers/azurerm/resource_arm_virtual_machine.go
@@ -808,9 +808,11 @@ func resourceArmVirtualMachineStorageOsDiskHash(v interface{}) int {
 	if m["vhd_uri"] != nil {
 		buf.WriteString(fmt.Sprintf("%s-", m["vhd_uri"].(string)))
 	}
-	managedDisk := m["managed_disk"].(map[string]interface{})
-	if managedDisk["storage_account_type"] != nil {
-		buf.WriteString(fmt.Sprintf("%s-", managedDisk["storage_account_type"].(string)))
+	if m["managed_disk"] != nil {
+		managedDisk := m["managed_disk"].(map[string]interface{})
+		if managedDisk["storage_account_type"] != nil {
+			buf.WriteString(fmt.Sprintf("%s-", managedDisk["storage_account_type"].(string)))
+		}
 	}
 	return hashcode.String(buf.String())
 }