diff --git a/src/backend/catalog/partition.c b/src/backend/catalog/partition.c
new file mode 100644
index eb35fab..aa9c70d
*** a/src/backend/catalog/partition.c
--- b/src/backend/catalog/partition.c
*************** partition_list_bounds_merge(int partnatt
*** 3110,3116 ****
--- 3110,3119 ----
  			 */
  			if (jointype == JOIN_INNER || jointype == JOIN_RIGHT ||
  				jointype == JOIN_SEMI)
+ 			{
  				merged_index = -1;
+ 				merged_datum = NULL;
+ 			}
  			else if (jointype == JOIN_LEFT || jointype == JOIN_FULL ||
  					 jointype == JOIN_ANTI)
  			{
*************** partition_list_bounds_merge(int partnatt
*** 3140,3146 ****
--- 3143,3152 ----
  			 */
  			if (jointype == JOIN_INNER || jointype == JOIN_LEFT ||
  				jointype == JOIN_SEMI || jointype == JOIN_ANTI)
+ 			{
  				merged_index = -1;
+ 				merged_datum = NULL;
+ 			}
  			else if (jointype == JOIN_RIGHT || jointype == JOIN_FULL)
  			{
  				/*
*************** map_and_merge_partitions(int *partmap1,
*** 3334,3346 ****
  
  	/*
  	 * If the given to partitions map to each other, find the corresponding
! 	 * merged partition index .
  	 */
  	if (partmap1[index1] == index2 && partmap2[index2] == index1)
  	{
  		/*
! 		 * If both the partitions are mapped to the same merged partition, get
! 		 * the index of merged partition.
  		 */
  		if (mergemap1[index1] == mergemap2[index2])
  		{
--- 3340,3352 ----
  
  	/*
  	 * If the given to partitions map to each other, find the corresponding
! 	 * merged partition index.
  	 */
  	if (partmap1[index1] == index2 && partmap2[index2] == index1)
  	{
  		/*
! 		 * If both the partitions are mapped to the same merged partition, or
! 		 * neither maps at all yet, get the index of merged partition.
  		 */
  		if (mergemap1[index1] == mergemap2[index2])
  		{
*************** map_and_merge_partitions(int *partmap1,
*** 3352,3359 ****
  			 */
  			if (merged_index < 0)
  			{
! 				merged_index = *next_index;
! 				*next_index = *next_index + 1;
  				mergemap1[index1] = merged_index;
  				mergemap2[index2] = merged_index;
  			}
--- 3358,3364 ----
  			 */
  			if (merged_index < 0)
  			{
! 				merged_index = (*next_index)++;
  				mergemap1[index1] = merged_index;
  				mergemap2[index2] = merged_index;
  			}
*************** map_and_merge_partitions(int *partmap1,
*** 3366,3380 ****
  		 * partitions map to the same merged partition.
  		 */
  		else if (mergemap1[index1] >= 0 && mergemap2[index2] < 0)
! 		{
! 			mergemap2[index2] = mergemap1[index1];
! 			merged_index = mergemap1[index1];
! 		}
  		else if (mergemap1[index1] < 0 && mergemap2[index2] >= 0)
! 		{
! 			mergemap1[index1] = mergemap2[index2];
! 			merged_index = mergemap2[index2];
! 		}
  		else
  		{
  			Assert(mergemap1[index1] != mergemap2[index2] &&
--- 3371,3379 ----
  		 * partitions map to the same merged partition.
  		 */
  		else if (mergemap1[index1] >= 0 && mergemap2[index2] < 0)
! 			merged_index = mergemap2[index2] = mergemap1[index1];
  		else if (mergemap1[index1] < 0 && mergemap2[index2] >= 0)
! 			merged_index = mergemap1[index1] = mergemap2[index2];
  		else
  		{
  			Assert(mergemap1[index1] != mergemap2[index2] &&