diff --git a/fpdfsdk/fpdf_ppo.cpp b/fpdfsdk/fpdf_ppo.cpp
index 059abd6..2cd86d6 100644
--- a/fpdfsdk/fpdf_ppo.cpp
+++ b/fpdfsdk/fpdf_ppo.cpp
@@ -289,6 +289,8 @@
     m_ObjectNumberMap[dwOldPageObj] = dwNewPageObj;
   }
 
+  void ClearObjectNumberMap() { m_ObjectNumberMap.clear(); }
+
  private:
   uint32_t GetNewObjId(CPDF_Reference* pRef);
 
@@ -598,7 +600,7 @@
   if (!safe_numPagesPerSheet.IsValid())
     return false;
 
-  m_ObjectNumberMap.clear();
+  ClearObjectNumberMap();
   m_SrcPageXObjectMap.clear();
   size_t numPagesPerSheet = safe_numPagesPerSheet.ValueOrDie();
   NupState nupState(destPageSize, numPagesOnXAxis, numPagesOnYAxis);