diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 81ba024bba..110c594edd 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -2300,7 +2300,27 @@ ExecWindowAgg(PlanState *pstate)
 						continue;
 					}
 					else
+					{
 						winstate->status = WINDOWAGG_PASSTHROUGH;
+
+						/*
+						 * Otherwise, if we're not the top-window, we'd better
+						 * NULLify the aggregate results, else, by-ref result
+						 * types will point to freed memory.  We can get away
+						 * without storing the final result of the WindowFunc
+						 * because in the planner we insisted that the
+						 * runcondition is strict.  Setting these to NULL will
+						 * ensure the top-level WindowAgg filter will always
+						 * filter out the rows produced in this WindowAgg when
+						 * not in WINDOWAGG_RUN state.
+						 */
+						numfuncs = winstate->numfuncs;
+						for (i = 0; i < numfuncs; i++)
+						{
+							econtext->ecxt_aggvalues[i] = (Datum) 0;
+							econtext->ecxt_aggnulls[i] = true;
+						}
+					}
 				}
 				else
 				{
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 4ddaed31a4..a25956200e 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2399,6 +2399,22 @@ check_and_push_window_quals(Query *subquery, RangeTblEntry *rte, Index rti,
 	if (list_length(opexpr->args) != 2)
 		return true;
 
+	/*
+	 * Currently, we restrict this optimization to strict OpExprs.  The reason
+	 * for this is that during execution, once we stop evaluating WindowFuncs
+	 * on lower-level WindowAgg nodes, since we're no longer updating them,
+	 * we NULLify the aggregate and window aggregate results to prevent by-ref
+	 * result typed window aggregates from pointing to free'd memory (this can
+	 * happen on non-FLOAT8PASSBYVAL builds).  Upper-level WindowAgg nodes may
+	 * make reference to these results in their filter clause and we can
+	 * ensure the filter remain false by making sure the operator is strict
+	 * and by performing the NULLification when the run-condition is no longer
+	 * true.
+	 */
+	set_opfuncid(opexpr);
+	if (!func_strict(opexpr->opfuncid))
+		return false;
+
 	/*
 	 * Check for plain Vars that reference window functions in the subquery.
 	 * If we find any, we'll ask find_window_run_conditions() if 'opexpr' can