diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index b849ae03b8..6f3a4a063c 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -146,9 +146,6 @@ static double get_number_of_groups(PlannerInfo *root,
 					 double path_rows,
 					 grouping_sets_data *gd,
 					 List *target_list);
-static Size estimate_hashagg_tablesize(Path *path,
-						   const AggClauseCosts *agg_costs,
-						   double dNumGroups);
 static RelOptInfo *create_grouping_paths(PlannerInfo *root,
 					  RelOptInfo *input_rel,
 					  PathTarget *target,
@@ -3634,40 +3631,6 @@ get_number_of_groups(PlannerInfo *root,
 }
 
 /*
- * estimate_hashagg_tablesize
- *	  estimate the number of bytes that a hash aggregate hashtable will
- *	  require based on the agg_costs, path width and dNumGroups.
- *
- * XXX this may be over-estimating the size now that hashagg knows to omit
- * unneeded columns from the hashtable. Also for mixed-mode grouping sets,
- * grouping columns not in the hashed set are counted here even though hashagg
- * won't store them. Is this a problem?
- */
-static Size
-estimate_hashagg_tablesize(Path *path, const AggClauseCosts *agg_costs,
-						   double dNumGroups)
-{
-	Size		hashentrysize;
-
-	/* Estimate per-hash-entry space at tuple width... */
-	hashentrysize = MAXALIGN(path->pathtarget->width) +
-		MAXALIGN(SizeofMinimalTupleHeader);
-
-	/* plus space for pass-by-ref transition values... */
-	hashentrysize += agg_costs->transitionSpace;
-	/* plus the per-hash-entry overhead */
-	hashentrysize += hash_agg_entry_size(agg_costs->numAggs);
-
-	/*
-	 * Note that this disregards the effect of fill-factor and growth policy
-	 * of the hash-table. That's probably ok, given default the default
-	 * fill-factor is relatively high. It'd be hard to meaningfully factor in
-	 * "double-in-size" growth policies here.
-	 */
-	return hashentrysize * dNumGroups;
-}
-
-/*
  * create_grouping_paths
  *
  * Build a new upperrel containing Paths for grouping and/or aggregation.
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index e8f51d2d0d..be059f0de0 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -114,6 +114,7 @@
 #include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_type.h"
 #include "executor/executor.h"
+#include "executor/nodeAgg.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -3902,6 +3903,39 @@ estimate_hash_bucket_stats(PlannerInfo *root, Node *hashkey, double nbuckets,
 	ReleaseVariableStats(vardata);
 }
 
+/*
+ * estimate_hashagg_tablesize
+ *	  estimate the number of bytes that a hash aggregate hashtable will
+ *	  require based on the agg_costs, path width and dNumGroups.
+ *
+ * XXX this may be over-estimating the size now that hashagg knows to omit
+ * unneeded columns from the hashtable. Also for mixed-mode grouping sets,
+ * grouping columns not in the hashed set are counted here even though hashagg
+ * won't store them. Is this a problem?
+ */
+Size
+estimate_hashagg_tablesize(Path *path, const AggClauseCosts *agg_costs,
+						   double dNumGroups)
+{
+	Size		hashentrysize;
+
+	/* Estimate per-hash-entry space at tuple width... */
+	hashentrysize = MAXALIGN(path->pathtarget->width) +
+		MAXALIGN(SizeofMinimalTupleHeader);
+
+	/* plus space for pass-by-ref transition values... */
+	hashentrysize += agg_costs->transitionSpace;
+	/* plus the per-hash-entry overhead */
+	hashentrysize += hash_agg_entry_size(agg_costs->numAggs);
+
+	/*
+	 * Note that this disregards the effect of fill-factor and growth policy
+	 * of the hash-table. That's probably ok, given default the default
+	 * fill-factor is relatively high. It'd be hard to meaningfully factor in
+	 * "double-in-size" growth policies here.
+	 */
+	return hashentrysize * dNumGroups;
+}
 
 /*-------------------------------------------------------------------------
  *
diff --git a/src/include/utils/selfuncs.h b/src/include/utils/selfuncs.h
index 5cc4cf15e2..e65ab13b1a 100644
--- a/src/include/utils/selfuncs.h
+++ b/src/include/utils/selfuncs.h
@@ -213,6 +213,9 @@ extern void estimate_hash_bucket_stats(PlannerInfo *root,
 						   Node *hashkey, double nbuckets,
 						   Selectivity *mcv_freq,
 						   Selectivity *bucketsize_frac);
+extern Size estimate_hashagg_tablesize(Path *path,
+						   const AggClauseCosts *agg_costs,
+						   double dNumGroups);
 
 extern List *deconstruct_indexquals(IndexPath *path);
 extern void genericcostestimate(PlannerInfo *root, IndexPath *path,