diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index fb6ce49056..221a34e738 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -1673,7 +1673,19 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 				pprune->subpart_map = palloc(sizeof(int) * partdesc->nparts);
 				for (pp_idx = 0; pp_idx < partdesc->nparts; ++pp_idx)
 				{
-					if (pinfo->relid_map[pd_idx] != partdesc->oids[pp_idx])
+					/*
+					 * pinfo->relid_map can contain InvalidOid entries for
+					 * partitions pruned by the planner.  We cannot tell
+					 * exactly which of the partdesc entries these correspond
+					 * to, but we don't have to; just skip over them.  The
+					 * non-pruned relid_map entries, however, had better be a
+					 * subset of the partdesc entries and in the same order.
+					 */
+					while (pd_idx < pinfo->nparts &&
+						   !OidIsValid(pinfo->relid_map[pd_idx]))
+						pd_idx++;
+					if (pd_idx >= pinfo->nparts ||
+						pinfo->relid_map[pd_idx] != partdesc->oids[pp_idx])
 					{
 						pprune->subplan_map[pp_idx] = -1;
 						pprune->subpart_map[pp_idx] = -1;
@@ -1686,6 +1698,14 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 							pinfo->subpart_map[pd_idx++];
 					}
 				}
+
+				/*
+				 * It might seem that we need to skip any trailing InvalidOid
+				 * entries in pinfo->relid_map before asserting that we
+				 * scanned all of the relid_map.  But we will have skipped
+				 * them above, because they must correspond to some
+				 * partdesc->oids entries; we just couldn't tell which.
+				 */
 				Assert(pd_idx == pinfo->nparts);
 			}