diff --git a/nova/exception.py b/nova/exception.py
index 234d502b9f6a..3669eacc7a3e 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -1966,12 +1966,22 @@ class CPUPinningNotSupported(Invalid):
 
 
 class CPUPinningInvalid(Invalid):
-    msg_fmt = _("Cannot pin/unpin cpus %(requested)s from the following "
-                "pinned set %(pinned)s")
+    msg_fmt = _("CPU set to pin %(requested)s must be a subset of "
+                "free CPU set %(free)s")
+
+
+class CPUUnpinningInvalid(Invalid):
+    msg_fmt = _("CPU set to unpin %(requested)s must be a subset of "
+                "pinned CPU set %(pinned)s")
 
 
 class CPUPinningUnknown(Invalid):
-    msg_fmt = _("CPU set to pin/unpin %(requested)s must be a subset of "
+    msg_fmt = _("CPU set to pin %(requested)s must be a subset of "
+                "known CPU set %(cpuset)s")
+
+
+class CPUUnpinningUnknown(Invalid):
+    msg_fmt = _("CPU set to unpin %(requested)s must be a subset of "
                 "known CPU set %(cpuset)s")
 
 
diff --git a/nova/objects/numa.py b/nova/objects/numa.py
index 86ca18faa32d..15703e656522 100644
--- a/nova/objects/numa.py
+++ b/nova/objects/numa.py
@@ -82,16 +82,17 @@ class NUMACell(base.NovaObject):
                                               cpuset=list(self.pinned_cpus))
         if self.pinned_cpus & cpus:
             raise exception.CPUPinningInvalid(requested=list(cpus),
-                                              pinned=list(self.pinned_cpus))
+                                              free=list(self.cpuset -
+                                                        self.pinned_cpus))
         self.pinned_cpus |= cpus
 
     def unpin_cpus(self, cpus):
         if cpus - self.cpuset:
-            raise exception.CPUPinningUnknown(requested=list(cpus),
-                                              cpuset=list(self.pinned_cpus))
+            raise exception.CPUUnpinningUnknown(requested=list(cpus),
+                                                cpuset=list(self.pinned_cpus))
         if (self.pinned_cpus & cpus) != cpus:
-            raise exception.CPUPinningInvalid(requested=list(cpus),
-                                              pinned=list(self.pinned_cpus))
+            raise exception.CPUUnpinningInvalid(requested=list(cpus),
+                                                pinned=list(self.pinned_cpus))
         self.pinned_cpus -= cpus
 
     def pin_cpus_with_siblings(self, cpus):
diff --git a/nova/tests/unit/objects/test_numa.py b/nova/tests/unit/objects/test_numa.py
index 61b7f4ec02bf..1e1bf76e7148 100644
--- a/nova/tests/unit/objects/test_numa.py
+++ b/nova/tests/unit/objects/test_numa.py
@@ -93,9 +93,9 @@ class _TestNUMA(object):
                           numacell.pin_cpus, set([1, 55]))
         self.assertRaises(exception.CPUPinningInvalid,
                           numacell.pin_cpus, set([1, 4]))
-        self.assertRaises(exception.CPUPinningUnknown,
+        self.assertRaises(exception.CPUUnpinningUnknown,
                           numacell.unpin_cpus, set([1, 55]))
-        self.assertRaises(exception.CPUPinningInvalid,
+        self.assertRaises(exception.CPUUnpinningInvalid,
                           numacell.unpin_cpus, set([1, 4]))
         numacell.unpin_cpus(set([1, 2, 3]))
         self.assertEqual(set([1, 2, 3, 4]), numacell.free_cpus)
@@ -111,13 +111,13 @@ class _TestNUMA(object):
         self.assertEqual(set(), numacell.free_cpus)
         numacell.unpin_cpus_with_siblings(set([1]))
         self.assertEqual(set([1, 3]), numacell.free_cpus)
-        self.assertRaises(exception.CPUPinningInvalid,
+        self.assertRaises(exception.CPUUnpinningInvalid,
                           numacell.unpin_cpus_with_siblings,
                           set([3]))
         self.assertRaises(exception.CPUPinningInvalid,
                           numacell.pin_cpus_with_siblings,
                           set([4]))
-        self.assertRaises(exception.CPUPinningInvalid,
+        self.assertRaises(exception.CPUUnpinningInvalid,
                           numacell.unpin_cpus_with_siblings,
                           set([3, 4]))
         self.assertEqual(set([1, 3]), numacell.free_cpus)