diff --git a/php/src/file/csv/CsvBuilder.php b/php/src/file/csv/CsvBuilder.php
index 24899b9..ef30d2c 100644
--- a/php/src/file/csv/CsvBuilder.php
+++ b/php/src/file/csv/CsvBuilder.php
@@ -26,7 +26,7 @@ class CsvBuilder extends AbstractBuilder {
   }
 
   protected function _checkOk(): bool {
-    $size = $this->ftell();
+    $this->size = $size = $this->ftell();
     if ($size === 0) return false;
     $this->rewind();
     return true;
diff --git a/php/src/file/tab/AbstractBuilder.php b/php/src/file/tab/AbstractBuilder.php
index 45c1cd9..4514442 100644
--- a/php/src/file/tab/AbstractBuilder.php
+++ b/php/src/file/tab/AbstractBuilder.php
@@ -131,6 +131,8 @@ abstract class AbstractBuilder extends TempStream implements IBuilder {
 
   protected bool $built = false, $closed = false;
 
+  protected ?int $size = null;
+
   function build(?iterable $rows=null, bool $close=true): bool {
     $ok = true;
     if (!$this->built) {
@@ -155,6 +157,10 @@ abstract class AbstractBuilder extends TempStream implements IBuilder {
     if ($output !== null) {
       http::download_as(path::filename($output));
     }
+    $size = $this->size;
+    if ($size !== null) {
+      header("Content-Length: $size");
+    }
     $this->sentHeaders = true;
   }