diff --git a/src/future/exec/ExecFuture.php b/src/future/exec/ExecFuture.php
--- a/src/future/exec/ExecFuture.php
+++ b/src/future/exec/ExecFuture.php
@@ -817,7 +817,18 @@
         $max_stderr_read_bytes);
     }
 
+    $is_done = false;
     if (!$status['running']) {
+      // We may still have unread bytes on stdout or stderr, particularly if
+      // this future is being buffered and streamed. If we do, we don't want to
+      // consider the subprocess to have exited until we've read everything.
+      // See T9724 for context.
+      if (feof($stdout) && feof($stderr)) {
+        $is_done = true;
+      }
+    }
+
+    if ($is_done) {
       if ($this->useWindowsFileStreams) {
         fclose($stdout);
         fclose($stderr);
diff --git a/src/future/exec/__tests__/ExecFutureTestCase.php b/src/future/exec/__tests__/ExecFutureTestCase.php
--- a/src/future/exec/__tests__/ExecFutureTestCase.php
+++ b/src/future/exec/__tests__/ExecFutureTestCase.php
@@ -150,6 +150,9 @@
 
     // We expect to get the entire string back in the read.
     $this->assertEqual($str_len_4, $read);
+
+    // Remove the limit so we can resolve the future.
+    $future->setReadBufferSize(null);
     $future->resolve();
   }