diff --git a/fpdfsdk/cpdfsdk_formfillenvironment.cpp b/fpdfsdk/cpdfsdk_formfillenvironment.cpp
index 6d3aab3..f016ff4 100644
--- a/fpdfsdk/cpdfsdk_formfillenvironment.cpp
+++ b/fpdfsdk/cpdfsdk_formfillenvironment.cpp
@@ -278,7 +278,7 @@
                                           TimerCallback lpTimerFunc) {
   if (m_pInfo && m_pInfo->FFI_SetTimer)
     return m_pInfo->FFI_SetTimer(m_pInfo, uElapse, lpTimerFunc);
-  return -1;
+  return CFX_SystemHandler::kInvalidTimerID;
 }
 
 void CPDFSDK_FormFillEnvironment::KillTimer(int nTimerID) {