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
@@ -528,6 +528,7 @@
     'nonempty' => 'utils/utils.php',
     'phlog' => 'error/phlog.php',
     'pht' => 'internationalization/pht.php',
+    'phutil_build_http_querystring' => 'utils/utils.php',
     'phutil_censor_credentials' => 'utils/utils.php',
     'phutil_console_confirm' => 'console/format.php',
     'phutil_console_format' => 'console/format.php',
diff --git a/src/future/http/BaseHTTPFuture.php b/src/future/http/BaseHTTPFuture.php
--- a/src/future/http/BaseHTTPFuture.php
+++ b/src/future/http/BaseHTTPFuture.php
@@ -273,7 +273,7 @@
       return strlen($data);
     }
 
-    return strlen(http_build_query($data, '', '&'));
+    return strlen(phutil_build_http_querystring($data));
   }
 
 
diff --git a/src/future/http/HTTPFuture.php b/src/future/http/HTTPFuture.php
--- a/src/future/http/HTTPFuture.php
+++ b/src/future/http/HTTPFuture.php
@@ -244,7 +244,7 @@
 
     if ($this->getMethod() == 'GET') {
       if (is_array($data)) {
-        $data = http_build_query($data, '', '&');
+        $data = phutil_build_http_querystring($data);
         if (strpos($uri, '?') !== false) {
           $uri .= '&'.$data;
         } else {
@@ -254,7 +254,7 @@
       }
     } else {
       if (is_array($data)) {
-        $data = http_build_query($data, '', '&')."\r\n";
+        $data = phutil_build_http_querystring($data)."\r\n";
         $add_headers[] = array(
           'Content-Type',
           'application/x-www-form-urlencoded',
diff --git a/src/future/http/HTTPSFuture.php b/src/future/http/HTTPSFuture.php
--- a/src/future/http/HTTPSFuture.php
+++ b/src/future/http/HTTPSFuture.php
@@ -523,7 +523,7 @@
       // If we don't have any files, just encode the data as a query string,
       // make sure it's not including any files, and we're good to go.
       if (is_array($data)) {
-        $data = http_build_query($data, '', '&');
+        $data = phutil_build_http_querystring($data);
       }
 
       $this->checkForDangerousCURLMagic($data, $is_query_string = true);
diff --git a/src/markup/engine/remarkup/blockrule/PhutilRemarkupTestInterpreterRule.php b/src/markup/engine/remarkup/blockrule/PhutilRemarkupTestInterpreterRule.php
--- a/src/markup/engine/remarkup/blockrule/PhutilRemarkupTestInterpreterRule.php
+++ b/src/markup/engine/remarkup/blockrule/PhutilRemarkupTestInterpreterRule.php
@@ -11,7 +11,7 @@
     return sprintf(
       "Content: (%s)\nArgv: (%s)",
       $content,
-      http_build_query($argv));
+      phutil_build_http_querystring($argv));
   }
 
 }
diff --git a/src/parser/PhutilURI.php b/src/parser/PhutilURI.php
--- a/src/parser/PhutilURI.php
+++ b/src/parser/PhutilURI.php
@@ -174,7 +174,7 @@
     }
 
     if ($this->query) {
-      $query = '?'.http_build_query($this->query, '', '&');
+      $query = '?'.phutil_build_http_querystring($this->query, '', '&');
     } else {
       $query = null;
     }
diff --git a/src/utils/utils.php b/src/utils/utils.php
--- a/src/utils/utils.php
+++ b/src/utils/utils.php
@@ -1537,3 +1537,14 @@
 
   return ($bits === 0);
 }
+
+
+/**
+ * Build a query string from a dictionary.
+ *
+ * @param map<string, string> Dictionary of parameters.
+ * @return string HTTP query string.
+ */
+function phutil_build_http_querystring(array $parameters) {
+  return http_build_query($parameters, '', '&');
+}