diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -372,6 +372,7 @@
     'PhutilPygmentsSyntaxHighlighter' => 'markup/syntax/highlighter/PhutilPygmentsSyntaxHighlighter.php',
     'PhutilPythonFragmentLexer' => 'lexer/PhutilPythonFragmentLexer.php',
     'PhutilQsprintfInterface' => 'xsprintf/PhutilQsprintfInterface.php',
+    'PhutilQueryString' => 'xsprintf/PhutilQueryString.php',
     'PhutilQueryStringParser' => 'parser/PhutilQueryStringParser.php',
     'PhutilQueryStringParserTestCase' => 'parser/__tests__/PhutilQueryStringParserTestCase.php',
     'PhutilRainbowSyntaxHighlighter' => 'markup/syntax/highlighter/PhutilRainbowSyntaxHighlighter.php',
@@ -1023,6 +1024,7 @@
     'PhutilPygmentizeParserTestCase' => 'PhutilTestCase',
     'PhutilPygmentsSyntaxHighlighter' => 'Phobject',
     'PhutilPythonFragmentLexer' => 'PhutilLexer',
+    'PhutilQueryString' => 'Phobject',
     'PhutilQueryStringParser' => 'Phobject',
     'PhutilQueryStringParserTestCase' => 'PhutilTestCase',
     'PhutilRainbowSyntaxHighlighter' => 'Phobject',
diff --git a/src/xsprintf/PhutilQueryString.php b/src/xsprintf/PhutilQueryString.php
new file mode 100644
--- /dev/null
+++ b/src/xsprintf/PhutilQueryString.php
@@ -0,0 +1,39 @@
+<?php
+
+final class PhutilQueryString extends Phobject {
+
+  private $escaper;
+  private $argv;
+
+  public function __construct(PhutilQsprintfInterface $escaper, array $argv) {
+    $this->escaper = $escaper;
+    $this->argv = $argv;
+
+    // This makes sure we throw immediately if there are errors in the
+    // parameters.
+    $this->getMaskedString();
+  }
+
+  public function __toString() {
+    return $this->getMaskedString();
+  }
+
+  public function getUnmaskedString() {
+    return $this->renderString(true);
+  }
+
+  public function getMaskedString() {
+    return $this->renderString(false);
+  }
+
+  private function renderString($unmasked) {
+    return xsprintf(
+      'xsprintf_query',
+      array(
+        'escaper' => $this->escaper,
+        'unmasked' => $unmasked,
+      ),
+      $this->argv);
+  }
+
+}
diff --git a/src/xsprintf/qsprintf.php b/src/xsprintf/qsprintf.php
--- a/src/xsprintf/qsprintf.php
+++ b/src/xsprintf/qsprintf.php
@@ -61,12 +61,12 @@
 function qsprintf(PhutilQsprintfInterface $escaper, $pattern /* , ... */) {
   $args = func_get_args();
   array_shift($args);
-  return xsprintf('xsprintf_query', $escaper, $args);
+  return new PhutilQueryString($escaper, $args);
 }
 
 function vqsprintf(PhutilQsprintfInterface $escaper, $pattern, array $argv) {
   array_unshift($argv, $pattern);
-  return xsprintf('xsprintf_query', $escaper, $argv);
+  return new PhutilQueryString($escaper, $argv);
 }
 
 /**
@@ -74,12 +74,19 @@
  * @{function:qsprintf}.
  */
 function xsprintf_query($userdata, &$pattern, &$pos, &$value, &$length) {
-  $type    = $pattern[$pos];
-  $escaper = $userdata;
-  $next    = (strlen($pattern) > $pos + 1) ? $pattern[$pos + 1] : null;
+  $type = $pattern[$pos];
 
+  if (is_array($userdata)) {
+    $escaper = $userdata['escaper'];
+    $unmasked = $userdata['unmasked'];
+  } else {
+    $escaper = $userdata;
+    $unmasked = false;
+  }
+
+  $next = (strlen($pattern) > $pos + 1) ? $pattern[$pos + 1] : null;
   $nullable = false;
-  $done     = false;
+  $done = false;
 
   $prefix   = '';
 
@@ -190,6 +197,9 @@
         break;
 
       case 'Q': // Query Fragment
+        if ($value instanceof PhutilQueryString) {
+          $value = $value->getUnmaskedString();
+        }
         $type = 's';
         break;
 
@@ -287,6 +297,24 @@
 function qsprintf_check_scalar_type($value, $type, $query) {
   switch ($type) {
     case 'Q':
+      // TODO: See T13217. Remove this eventually.
+      if (is_string($value)) {
+        phlog(
+          pht(
+            'UNSAFE: Raw string ("%s") passed to query ("%s") for "%%Q" '.
+            'conversion. %%Q should be passed a query string.',
+            $value,
+            $query));
+        break;
+      }
+
+      if (!($value instanceof PhutilQueryString)) {
+        throw new AphrontParameterQueryException(
+          $query,
+          pht('Expected a PhutilQueryString for %%%s conversion.', $type));
+      }
+      break;
+
     case 'LC':
     case 'T':
     case 'C':
diff --git a/src/xsprintf/queryfx.php b/src/xsprintf/queryfx.php
--- a/src/xsprintf/queryfx.php
+++ b/src/xsprintf/queryfx.php
@@ -4,6 +4,8 @@
   $argv = func_get_args();
   $query = call_user_func_array('qsprintf', $argv);
 
+  $query = $query->getUnmaskedString();
+
   $conn->setLastActiveEpoch(time());
   $conn->executeRawQuery($query);
 }