diff --git a/html/inc/util_ops.inc b/html/inc/util_ops.inc
index 339f36f483..55d48faff6 100644
--- a/html/inc/util_ops.inc
+++ b/html/inc/util_ops.inc
@@ -244,16 +244,14 @@ function test_mysql_query($msg) {
 // - for any results w/ server state UNSENT, set server state to OVER
 // - set the CANCELLED bit in workunit.error_mask
 //
-function cancel_wu($wuid1, $wuid2) {
-    $command1="update result set server_state=5, outcome=5 where server_state=2 and $wuid1<=workunitid and workunitid<=$wuid2";
-    $command2="update workunit set error_mask=error_mask|16 where $wuid1<=id and id<=$wuid2";
-
-    if (!mysql_query($command1)) {
-        echo "MySQL command $command1 failed:<br/>unable to cancel unsent results.<br/>";
-        return 1;
-    } else if (!mysql_query($command2)) {
-        echo "MySQL command $command2 failed:<br/>unable to cancel workunits.<br/>";
-        return 2;
+function cancel_wus($wuid1, $wuid2) {
+    $query="update result set server_state=5, outcome=5 where server_state=2 and $wuid1<=workunitid and workunitid<=$wuid2";
+    if (!mysql_query($query)) {
+        error_page("DB query $query failed");
+    }
+    $query="update workunit set error_mask=error_mask|16 where $wuid1<=id and id<=$wuid2";
+    if (!mysql_query($query)) {
+        error_page("DB query $query failed");
     }
 
     // trigger the transitioner (it will set file_delete_state)
@@ -261,20 +259,26 @@ function cancel_wu($wuid1, $wuid2) {
     $now = time();
     $query="update workunit set transition_time=$now where $wuid1<=id and id<=$wuid2";
     mysql_query($query);
-
     return 0;
 }
 
 // like above, but if a workunit has a result that's already sent,
-// don't cancel it
+// don't cancel the workunit
 //
-function cancel_wu_if_unsent($id1, $id2) {
+function cancel_wus_if_unsent($id1, $id2) {
     $wus = BoincWorkunit::enum("id >= $id1 and id <= $id2");
     foreach ($wus as $wu) {
         $results = BoincResult::enum("workunitid=$wu.id and server_state > 2");
         if (count($results)) continue;
-
+        $query="update result set server_state=5, outcome=5 where workunitid=$wu->id";
+        if (!mysql_query($query)) {
+            error_page("DB query $query failed");
+        }
+        if (!$wu->update("error_mask=error_mask|16")) {
+            error_page("WU update failed");
+        }
     }
+    return 0;
 }
 
 if (isset($cli_only)) {
diff --git a/html/ops/cancel_wu_action.php b/html/ops/cancel_wu_action.php
index 56ee8a1f94..e9264637de 100644
--- a/html/ops/cancel_wu_action.php
+++ b/html/ops/cancel_wu_action.php
@@ -24,31 +24,27 @@
 require_once("../inc/db.inc");
 require_once("../inc/util_ops.inc");
 
-admin_page_head("Cancel WU");
-
 db_init();
 
 $wuid1 = get_int('wuid1');
 $wuid2 = get_int('wuid2');
+$unsent_only = get_str('unsent_only', true);
 
 if ($wuid1<1 || $wuid2<$wuid1) {
-    echo "<h2>Workunit IDs fail to satisfy the conditions:<br/>
-        1 <= WU1 ($wuid1) <= WU2 ($wuid2)<br/>
-        Unable to process request to cancel workunits.
-        </h2>
-    ";
-    exit();
+    error_page(
+        "<h2>Workunit IDs fail to satisfy the conditions:<p> 0 < ID1 <= ID2"
+    );
 }
 
-echo "CANCELLING workunits $wuid1 to $wuid2 inclusive....<br/>";
-
-if (cancel_wu($wuid1, $wuid2)) {
-    echo "<h2>Failed in";
+if ($unsent_only) {
+    cancel_wus_if_unsent($wuid1, $wuid2);
 } else {
-    echo "<h2>Success in";
+    cancel_wus($wuid1, $wuid2);
 }
-echo " cancelling workunits $wuid1 <= WUID <= $wuid2</h2>";
 
+admin_page_head("Cancel jobs");
+echo " canceled jobs with $wuid1 <= workunit ID <= $wuid2</h2>";
 admin_page_tail();
+
 $cvs_version_tracker[]="\$Id$";  //Generated automatically - do not edit
 ?>
diff --git a/html/ops/cancel_wu_form.php b/html/ops/cancel_wu_form.php
index cb8e20f6dc..72b00ae3ad 100644
--- a/html/ops/cancel_wu_form.php
+++ b/html/ops/cancel_wu_form.php
@@ -20,20 +20,16 @@
 
 require_once("../inc/util_ops.inc");
 
-admin_page_head("Cancel workunit(s)");
+admin_page_head("Cancel jobs");
 
 echo "<form action=\"cancel_wu_action.php\">
 ";
 echo "<p>
-	This form may be used to cancel unnecessary or unwanted workunits.
-    We recommend that you stop the project before doing this.
-    Note that the workunits and their corresponding
-    results (if any) are NOT removed from the database.
+    We recommend that you stop the project before canceling jobs.
+    <p>
+    Canceled jobs are not removed from the database.
     Instead, they are marked as 'no longer needed'.
-    In most cases you should probably only remove workunits whose results
-    are all unsent,
-    since otherwise a user will not get credit
-    for a result that they might return.
+    <p>
     <p>
 ";
 // TODO: David, a query that shows all workunits that do not have all results unsent is:
@@ -42,9 +38,18 @@ echo "<p>
 // be useful to incorporate into this page.
 
 start_table();
-row2("First Workunit (ID) to cancel", "<input size=\"32\" name=\"wuid1\"");
-row2("Last  Workunit (ID) to cancel", "<input size=\"32\" name=\"wuid2\"");
-row2("", "<input type=\"submit\" value=\"CANCEL WORKUNITS\">");
+row2("Workunit ID of first job to cancel", "<input size=\"32\" name=\"wuid1\"");
+row2("Workunit ID of last job to cancel", "<input size=\"32\" name=\"wuid2\"");
+row2(
+    "Cancel only jobs with no instance in progress
+        <br><span class=note>
+        You can cancel jobs with instances that are in progress,
+        but if you do so, users will not get credit for these instances.
+        </span>
+    ",
+    "<input type=checkbox name=unsent_only>"
+);
+row2("", "<input type=\"submit\" value=\"Cancel jobs\">");
 end_table();
 echo "
     </form>
diff --git a/html/ops/cancel_wus.php b/html/ops/cancel_wus.php
index b1a422383b..821255f997 100644
--- a/html/ops/cancel_wus.php
+++ b/html/ops/cancel_wus.php
@@ -7,5 +7,5 @@ require_once("../inc/util_ops.inc");
 
 db_init();
 
-//cancel_wu(0, 636);
+//cancel_wus(0, 636);
 ?>