*** a/src/backend/access/index/indexam.c
--- b/src/backend/access/index/indexam.c
***************
*** 81,87 ****
  #define RELATION_CHECKS \
  ( \
  	AssertMacro(RelationIsValid(indexRelation)), \
! 	AssertMacro(PointerIsValid(indexRelation->rd_am)) \
  )
  
  #define SCAN_CHECKS \
--- 81,88 ----
  #define RELATION_CHECKS \
  ( \
  	AssertMacro(RelationIsValid(indexRelation)), \
! 	AssertMacro(PointerIsValid(indexRelation->rd_am)), \
! 	AssertMacro(!ReindexIsProcessingIndex(RelationGetRelid(indexRelation))) \
  )
  
  #define SCAN_CHECKS \