diff --git a/tools/python/xen/util/bugtool.py b/tools/python/xen/util/bugtool.py
index 18569dcb33..e8d96b884a 100644
--- a/tools/python/xen/util/bugtool.py
+++ b/tools/python/xen/util/bugtool.py
@@ -141,7 +141,7 @@ def getBugTitle(bug):
     finally:
         f.close()
 
-    raise "Could not find title of bug %d!" % bug
+    raise ValueError("Could not find title of bug %d!" % bug)
 
 
 def send(bug, conn, fd, filename, username, password):
diff --git a/tools/python/xen/xend/XendBase.py b/tools/python/xen/xend/XendBase.py
index 73fed471dc..924477669a 100644
--- a/tools/python/xen/xend/XendBase.py
+++ b/tools/python/xen/xend/XendBase.py
@@ -115,7 +115,7 @@ class XendBase:
             # In OSS, ref == uuid
             return uuid
         else:
-            raise "Big Error.. TODO!"
+            raise ValueError("Big Error.. TODO!")
 
     def get_all_records(cls):
         return dict([(inst.get_uuid(), inst.get_record())
diff --git a/tools/python/xen/xm/main.py b/tools/python/xen/xm/main.py
index e0e3d154b2..d7fd81be91 100644
--- a/tools/python/xen/xm/main.py
+++ b/tools/python/xen/xm/main.py
@@ -2796,7 +2796,7 @@ def xm_network_attach(args):
                              for ref, record in server.xenapi.network
                              .get_all_records().items()])
             if bridge not in networks.keys():
-                raise "Unknown bridge name!"
+                raise ValueError("Unknown bridge name!")
             return networks[bridge]
 
         vif_conv = {
diff --git a/tools/python/xen/xm/xenapi_create.py b/tools/python/xen/xm/xenapi_create.py
index ca8adc0a10..efe96ebd82 100644
--- a/tools/python/xen/xm/xenapi_create.py
+++ b/tools/python/xen/xm/xenapi_create.py
@@ -707,7 +707,7 @@ class sxp2xml:
                 vm.attributes['security_label'] = \
                                     security.set_security_label(sec_data[0][1][1],sec_data[0][2][1])
             except Exception, e:
-                raise "Invalid security data format: %s" % str(sec_data)
+                raise ValueError("Invalid security data format: %s" % str(sec_data))
 
         # Make the name tag