diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -9,7 +9,7 @@
   'names' => array(
     'conpherence.pkg.css' => '0e3cf785',
     'conpherence.pkg.js' => '020aebcf',
-    'core.pkg.css' => 'da792a0f',
+    'core.pkg.css' => '2e175364',
     'core.pkg.js' => '845355f4',
     'dark-console.pkg.js' => '187792c2',
     'differential.pkg.css' => '5c459f92',
@@ -115,7 +115,7 @@
     'rsrc/css/application/uiexample/example.css' => 'b4795059',
     'rsrc/css/core/core.css' => '1b29ed61',
     'rsrc/css/core/remarkup.css' => '7d3ebc86',
-    'rsrc/css/core/syntax.css' => '548567f6',
+    'rsrc/css/core/syntax.css' => '98fdb17e',
     'rsrc/css/core/z-index.css' => 'ac3bfcd4',
     'rsrc/css/diviner/diviner-shared.css' => '4bd263b0',
     'rsrc/css/font/font-awesome.css' => '3883938a',
@@ -909,7 +909,7 @@
     'sprite-login-css' => '18b368a6',
     'sprite-tokens-css' => 'f1896dc5',
     'syntax-default-css' => '055fc231',
-    'syntax-highlighting-css' => '548567f6',
+    'syntax-highlighting-css' => '98fdb17e',
     'tokens-css' => 'ce5a50bd',
     'trigger-rule' => '41b7b4f6',
     'trigger-rule-control' => '5faf27b9',
@@ -1422,9 +1422,6 @@
       'phuix-autocomplete',
       'javelin-mask',
     ),
-    '548567f6' => array(
-      'syntax-default-css',
-    ),
     '55a24e84' => array(
       'javelin-install',
       'javelin-dom',
@@ -1803,6 +1800,9 @@
       'javelin-request',
       'javelin-util',
     ),
+    '98fdb17e' => array(
+      'syntax-default-css',
+    ),
     '995f5102' => array(
       'javelin-install',
       'javelin-util',
diff --git a/src/applications/differential/parser/DifferentialChangesetParser.php b/src/applications/differential/parser/DifferentialChangesetParser.php
--- a/src/applications/differential/parser/DifferentialChangesetParser.php
+++ b/src/applications/differential/parser/DifferentialChangesetParser.php
@@ -1600,6 +1600,13 @@
           'span',
           array(
             'data-copy-text' => "\t",
+
+            // See PHI1814. Mark this as a single logical tab for the purposes
+            // of text selection behavior: when the user drags their mouse over
+            // the character sequence, we'd like the whole thing to select as
+            // a single unit.
+
+            'class' => 'logical-tab',
           ),
           str_repeat(' ', $ii));
         $tag = phutil_string_cast($tag);
diff --git a/src/applications/differential/parser/__tests__/DifferentialTabReplacementTestCase.php b/src/applications/differential/parser/__tests__/DifferentialTabReplacementTestCase.php
--- a/src/applications/differential/parser/__tests__/DifferentialTabReplacementTestCase.php
+++ b/src/applications/differential/parser/__tests__/DifferentialTabReplacementTestCase.php
@@ -4,8 +4,8 @@
   extends PhabricatorTestCase {
 
   public function testTabReplacement() {
-    $tab1 = "<span data-copy-text=\"\t\"> </span>";
-    $tab2 = "<span data-copy-text=\"\t\">  </span>";
+    $tab1 = "<span data-copy-text=\"\t\" class=\"logical-tab\"> </span>";
+    $tab2 = "<span data-copy-text=\"\t\" class=\"logical-tab\">  </span>";
 
     $cat = "\xF0\x9F\x90\xB1";
 
diff --git a/webroot/rsrc/css/core/syntax.css b/webroot/rsrc/css/core/syntax.css
--- a/webroot/rsrc/css/core/syntax.css
+++ b/webroot/rsrc/css/core/syntax.css
@@ -39,3 +39,8 @@
   color: #ffffff;
   cursor: default;
 }
+
+.logical-tab {
+  user-select: all;
+  -webkit-user-select: all;
+}