diff --git a/src/applications/differential/controller/DifferentialRevisionOperationController.php b/src/applications/differential/controller/DifferentialRevisionOperationController.php
--- a/src/applications/differential/controller/DifferentialRevisionOperationController.php
+++ b/src/applications/differential/controller/DifferentialRevisionOperationController.php
@@ -58,6 +58,48 @@
           $repository->getMonogram()));
     }
 
+    $op = new DrydockLandRepositoryOperation();
+
+    // Check for other operations. Eventually this should probably be more
+    // general (e.g., it's OK to land to multiple different branches
+    // simultaneously) but just put this in as a sanity check for now.
+    $other_operations = id(new DrydockRepositoryOperationQuery())
+      ->setViewer($viewer)
+      ->withObjectPHIDs(array($revision->getPHID()))
+      ->withOperationTypes(
+        array(
+          $op->getOperationConstant(),
+        ))
+      ->withOperationStates(
+        array(
+          DrydockRepositoryOperation::STATE_WAIT,
+          DrydockRepositoryOperation::STATE_WORK,
+          DrydockRepositoryOperation::STATE_DONE,
+        ))
+      ->execute();
+
+    if ($other_operations) {
+      $any_done = false;
+      foreach ($other_operations as $operation) {
+        if ($operation->isDone()) {
+          $any_done = true;
+          break;
+        }
+      }
+
+      if ($any_done) {
+        return $this->rejectOperation(
+          $revision,
+          pht('Already Complete'),
+          pht('This revision has already landed.'));
+      } else {
+        return $this->rejectOperation(
+          $revision,
+          pht('Already In Flight'),
+          pht('This revision is already landing.'));
+      }
+    }
+
     if ($request->isFormPost()) {
       // NOTE: The operation is locked to the current active diff, so if the
       // revision is updated before the operation applies nothing sneaky
@@ -65,8 +107,6 @@
 
       $diff = $revision->getActiveDiff();
 
-      $op = new DrydockLandRepositoryOperation();
-
       $operation = DrydockRepositoryOperation::initializeNewOperation($op)
         ->setAuthorPHID($viewer->getPHID())
         ->setObjectPHID($revision->getPHID())
diff --git a/src/applications/differential/controller/DifferentialRevisionViewController.php b/src/applications/differential/controller/DifferentialRevisionViewController.php
--- a/src/applications/differential/controller/DifferentialRevisionViewController.php
+++ b/src/applications/differential/controller/DifferentialRevisionViewController.php
@@ -1047,6 +1047,10 @@
     $operations = id(new DrydockRepositoryOperationQuery())
       ->setViewer($viewer)
       ->withObjectPHIDs(array($revision->getPHID()))
+      ->withOperationTypes(
+        array(
+          DrydockLandRepositoryOperation::OPCONST,
+        ))
       ->withOperationStates(
         array(
           DrydockRepositoryOperation::STATE_WAIT,
@@ -1058,7 +1062,16 @@
       return null;
     }
 
-    $operation = head(msort($operations, 'getID'));
+    $state_fail = DrydockRepositoryOperation::STATE_FAIL;
+
+    // We're going to show the oldest operation which hasn't failed, or the
+    // most recent failure if they're all failures.
+    $operations = msort($operations, 'getID');
+    foreach ($operations as $operation) {
+      if ($operation->getOperationState() != $state_fail) {
+        break;
+      }
+    }
 
     $box_view = id(new PHUIObjectBoxView())
       ->setHeaderText(pht('Active Operations'));
diff --git a/src/applications/drydock/query/DrydockRepositoryOperationQuery.php b/src/applications/drydock/query/DrydockRepositoryOperationQuery.php
--- a/src/applications/drydock/query/DrydockRepositoryOperationQuery.php
+++ b/src/applications/drydock/query/DrydockRepositoryOperationQuery.php
@@ -7,6 +7,7 @@
   private $objectPHIDs;
   private $repositoryPHIDs;
   private $operationStates;
+  private $operationTypes;
 
   public function withIDs(array $ids) {
     $this->ids = $ids;
@@ -33,6 +34,11 @@
     return $this;
   }
 
+  public function withOperationTypes(array $types) {
+    $this->operationTypes = $types;
+    return $this;
+  }
+
   public function newResultObject() {
     return new DrydockRepositoryOperation();
   }
@@ -139,6 +145,13 @@
         $this->operationStates);
     }
 
+    if ($this->operationTypes !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'operationType IN (%Ls)',
+        $this->operationTypes);
+    }
+
     return $where;
   }
 
diff --git a/src/applications/drydock/storage/DrydockRepositoryOperation.php b/src/applications/drydock/storage/DrydockRepositoryOperation.php
--- a/src/applications/drydock/storage/DrydockRepositoryOperation.php
+++ b/src/applications/drydock/storage/DrydockRepositoryOperation.php
@@ -158,6 +158,10 @@
     return false;
   }
 
+  public function isDone() {
+    return ($this->getOperationState() === self::STATE_DONE);
+  }
+
   public function getWorkingCopyMerges() {
     return $this->getImplementation()->getWorkingCopyMerges(
       $this);