diff --git a/src/rm/RequestManagerVirtualMachine.cc b/src/rm/RequestManagerVirtualMachine.cc
index d714a354dd..c6326536d2 100644
--- a/src/rm/RequestManagerVirtualMachine.cc
+++ b/src/rm/RequestManagerVirtualMachine.cc
@@ -3956,6 +3956,7 @@ Request::ErrorCode VirtualMachineBackup::request_execute(RequestAttributes& att,
     Backups::Mode mode;
     int li_id;
     int bk_id = -1;
+    long long backup_size = 0;
 
     // ------------------------------------------------------------------------
     // Get VM & Backup Information
@@ -3964,7 +3965,7 @@ Request::ErrorCode VirtualMachineBackup::request_execute(RequestAttributes& att,
     {
         vm->get_permissions(vm_perms);
 
-        vm->backup_size(quota_tmpl);
+        backup_size = vm->backup_size(quota_tmpl);
 
         mode  = vm->backups().mode();
         li_id = vm->backups().last_increment_id();
@@ -4005,6 +4006,16 @@ Request::ErrorCode VirtualMachineBackup::request_execute(RequestAttributes& att,
             return ACTION;
         }
 
+        long long free_mb;
+        bool check_capacity = ds->get_avail_mb(free_mb);
+
+        if (check_capacity && free_mb < backup_size)
+        {
+            att.resp_msg = "Not enough free space on target datastore";
+
+            return ACTION;
+        }
+
         ds->get_permissions(ds_perms);
     }
     else
diff --git a/src/vm/VirtualMachineDisk.cc b/src/vm/VirtualMachineDisk.cc
index fd422f7761..3d61bc0487 100644
--- a/src/vm/VirtualMachineDisk.cc
+++ b/src/vm/VirtualMachineDisk.cc
@@ -1571,19 +1571,14 @@ long long VirtualMachineDisks::backup_size(Template &ds_quotas, bool do_volatile
 {
     long long size = 0;
 
-    for (const auto disk : *this)
+    vector<int> ids;
+    backup_disk_ids(do_volatile, ids);
+
+    for (int id : ids)
     {
+        auto disk = get_disk(id);
         long long disk_size = 0;
 
-        string type = disk->vector_value("TYPE");
-
-        one_util::toupper(type);
-
-        if ((type == "SWAP") || ((type == "FS") && !do_volatile))
-        {
-            continue;
-        }
-
         disk->vector_value("SIZE", disk_size);
 
         size += disk_size;