diff --git a/cbuildbot/validation_pool.py b/cbuildbot/validation_pool.py
index 17dbae8..5949941 100644
--- a/cbuildbot/validation_pool.py
+++ b/cbuildbot/validation_pool.py
@@ -114,13 +114,6 @@
   """Raised if we try to apply a not-in-manifest change."""
 
 
-class PatchNotCommitReady(cros_patch.PatchException):
-  """Raised if a patch is not marked as commit ready."""
-
-  def ShortExplanation(self):
-    return 'isn\'t marked as Commit-Ready anymore.'
-
-
 class PatchModified(cros_patch.PatchException):
   """Raised if a patch is modified while the CQ is running."""
 
@@ -483,7 +476,7 @@
         if self._is_submitting:
           raise PatchRejected(dep_change)
         else:
-          raise PatchNotCommitReady(dep_change)
+          raise dep_change.GetMergeException() or PatchRejected(dep_change)
 
       unsatisfied.append(dep_change)
 
@@ -1670,13 +1663,7 @@
       raise TreeIsClosedException(closed_or_throttled=not throttled_ok)
 
     # Filter out changes that were modified during the CQ run.
-    unmodified_changes, errors = self.FilterModifiedChanges(changes)
-
-    # Filter out changes that aren't marked as CR=+2, CQ=+1, V=+1 anymore, in
-    # case the patch status changed during the CQ run.
-    filtered_changes = [x for x in unmodified_changes if x.IsMergeable()]
-    for change in set(unmodified_changes) - set(filtered_changes):
-      errors[change] = PatchNotCommitReady(change)
+    filtered_changes, errors = self.FilterModifiedChanges(changes)
 
     patch_series = PatchSeries(self.build_root, helper_pool=self._helper_pool,
                                is_submitting=True)
@@ -1739,8 +1726,8 @@
     Returns:
       This returns a tuple (unmodified_changes, errors).
 
-      unmodified_changes: A reloaded list of changes, only including unmodified
-                          and unsubmitted changes.
+      unmodified_changes: A reloaded list of changes, only including mergeable,
+                          unmodified and unsubmitted changes.
       errors: A dictionary. This dictionary will contain all patches that have
         encountered errors, and map them to the associated exception object.
     """
@@ -1749,15 +1736,18 @@
     # that occurs below will be mostly up-to-date.
     unmodified_changes, errors = [], {}
     reloaded_changes = list(cls.ReloadChanges(changes))
-    old_changes = cros_patch.PatchCache(changes)
-    for change in reloaded_changes:
-      if change.IsAlreadyMerged():
+    for change, reloaded_change in zip(changes, reloaded_changes):
+      if reloaded_change.IsAlreadyMerged():
         logging.warning('%s is already merged. It was most likely chumped '
                         'during the current CQ run.', change)
-      elif change.patch_number != old_changes[change].patch_number:
+      elif reloaded_change.patch_number != change.patch_number:
         # If users upload new versions of a CL while the CQ is in-flight, then
         # their CLs are no longer tested. These CLs should be rejected.
         errors[change] = PatchModified(change)
+      elif not reloaded_change.IsMergeable():
+        # Get the reason why this change is not mergeable anymore.
+        errors[change] = reloaded_change.GetMergeException()
+        errors[change].patch = change
       else:
         unmodified_changes.append(change)
 
diff --git a/cbuildbot/validation_pool_unittest.py b/cbuildbot/validation_pool_unittest.py
index 4e8fbc1..87848b0 100755
--- a/cbuildbot/validation_pool_unittest.py
+++ b/cbuildbot/validation_pool_unittest.py
@@ -1450,13 +1450,17 @@
     """Test that a CL is rejected if its approvals were pulled."""
     def _ReloadPatches(patches):
       reloaded = copy.deepcopy(patches)
-      self.PatchObject(reloaded[1], 'HasApproval', return_value=False)
+      approvals = {('VRIF', '1'): False}
+      backup = reloaded[1].HasApproval
+      self.PatchObject(
+          reloaded[1], 'HasApproval',
+          side_effect=lambda *args: approvals.get(args, backup(*args)))
       return reloaded
     self.PatchObject(gerrit, 'GetGerritPatchInfoWithPatchQueries',
                      _ReloadPatches)
     self.SubmitPool(submitted=self.patches[:1], rejected=self.patches[1:])
-    error = validation_pool.PatchNotCommitReady(self.patches[1])
-    self.assertEqualNotifyArg(error, self.patches[1], 'error')
+    message = 'CL:2 is not marked Verified=+1.'
+    self.assertEqualNotifyArg(message, self.patches[1], 'error')
 
   def testAlreadyMerged(self):
     """Test that a CL that was chumped during the run was not rejected."""
diff --git a/lib/patch.py b/lib/patch.py
index bead1bd..fb2ae7c 100644
--- a/lib/patch.py
+++ b/lib/patch.py
@@ -294,6 +294,18 @@
     return 'could not be found in the repo manifest.'
 
 
+class PatchNotMergeable(PatchException):
+  """Raised if a patch is not mergeable."""
+
+  def __init__(self, patch, reason):
+    PatchException.__init__(self, patch)
+    self.reason = str(reason)
+    self.args = (patch, reason)
+
+  def ShortExplanation(self):
+    return self.reason
+
+
 def MakeChangeId(unusable=False):
   """Create a random Change-Id.
 
@@ -1534,14 +1546,40 @@
 
   def IsMergeable(self):
     """Return true if all Gerrit approvals required for submission are set."""
-    return (self.status == 'NEW' and not self.WasVetoed() and
-            not self.IsDraft() and
-            self.HasApprovals({'CRVW': '2', 'VRIF': '1', 'COMR': ('1', '2')}))
+    return not self.GetMergeException()
 
   def HasReadyFlag(self):
     """Return true if the trybot-ready or commit-ready flag is set."""
     return self.HasApproval('COMR', ('1', '2')) or self.HasApproval('TRY', '1')
 
+  def GetMergeException(self):
+    """Return the reason why this change is not mergeable.
+
+    If the change is in fact mergeable, return None.
+    """
+    if self.IsDraft():
+      return PatchNotMergeable(self, 'is a draft.')
+
+    if self.status != 'NEW':
+      statuses = {
+        'MERGED': 'is already merged.',
+        'SUBMITTED': 'is being merged.',
+        'ABANDONED': 'is abandoned.',
+      }
+      message = statuses.get(self.status, 'has status %s.' % self.status)
+      return PatchNotMergeable(self, message)
+
+    if self.HasApproval('VRIF', '-1'):
+      return PatchNotMergeable(self, 'is marked as Verified=-1.')
+    elif self.HasApproval('CRVW', '-2'):
+      return PatchNotMergeable(self, 'is marked as Code-Review=-2.')
+    elif not self.HasApproval('CRVW', '2'):
+      return PatchNotMergeable(self, 'is not marked Code-Review=+2.')
+    elif not self.HasApproval('VRIF', '1'):
+      return PatchNotMergeable(self, 'is not marked Verified=+1.')
+    elif not self.HasApproval('COMR', ('1', '2')):
+      return PatchNotMergeable(self, 'is not marked Commit-Queue>=+1.')
+
   def GetLatestApproval(self, field):
     """Return most recent value of specific field on the current patchset.