diff --git a/src/backend/executor/nodeMergejoin.c b/src/backend/executor/nodeMergejoin.c
index bc036a30b0d..fdf2f4c1a85 100644
--- a/src/backend/executor/nodeMergejoin.c
+++ b/src/backend/executor/nodeMergejoin.c
@@ -230,19 +230,19 @@ MJExamineQuals(List *mergeclauses,
 				 qual->opno);
 
 		/* And get the matching support or comparison function */
+		Assert(clause->ssup.comparator == NULL);
 		sortfunc = get_opfamily_proc(opfamily,
 									 op_lefttype,
 									 op_righttype,
 									 BTSORTSUPPORT_PROC);
 		if (OidIsValid(sortfunc))
 		{
-			/* The sort support function should provide a comparator */
+			/* The sort support function can provide a comparator */
 			OidFunctionCall1(sortfunc, PointerGetDatum(&clause->ssup));
-			Assert(clause->ssup.comparator != NULL);
 		}
-		else
+		if (clause->ssup.comparator == NULL)
 		{
-			/* opfamily doesn't provide sort support, get comparison func */
+			/* support not available, get comparison func */
 			sortfunc = get_opfamily_proc(opfamily,
 										 op_lefttype,
 										 op_righttype,
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 4b5ef99531b..552e498cf57 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -245,62 +245,6 @@ get_ordering_op_properties(Oid opno,
 	return result;
 }
 
-/*
- * get_sort_function_for_ordering_op
- *		Get the OID of the datatype-specific btree sort support function,
- *		or if there is none, the btree comparison function,
- *		associated with an ordering operator (a "<" or ">" operator).
- *
- * *sortfunc receives the support or comparison function OID.
- * *issupport is set TRUE if it's a support func, FALSE if a comparison func.
- * *reverse is set FALSE if the operator is "<", TRUE if it's ">"
- * (indicating that comparison results must be negated before use).
- *
- * Returns TRUE if successful, FALSE if no btree function can be found.
- * (This indicates that the operator is not a valid ordering operator.)
- */
-bool
-get_sort_function_for_ordering_op(Oid opno, Oid *sortfunc,
-								  bool *issupport, bool *reverse)
-{
-	Oid			opfamily;
-	Oid			opcintype;
-	int16		strategy;
-
-	/* Find the operator in pg_amop */
-	if (get_ordering_op_properties(opno,
-								   &opfamily, &opcintype, &strategy))
-	{
-		/* Found a suitable opfamily, get matching support function */
-		*sortfunc = get_opfamily_proc(opfamily,
-									  opcintype,
-									  opcintype,
-									  BTSORTSUPPORT_PROC);
-		if (OidIsValid(*sortfunc))
-			*issupport = true;
-		else
-		{
-			/* opfamily doesn't provide sort support, get comparison func */
-			*sortfunc = get_opfamily_proc(opfamily,
-										  opcintype,
-										  opcintype,
-										  BTORDER_PROC);
-			if (!OidIsValid(*sortfunc)) /* should not happen */
-				elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
-					 BTORDER_PROC, opcintype, opcintype, opfamily);
-			*issupport = false;
-		}
-		*reverse = (strategy == BTGreaterStrategyNumber);
-		return true;
-	}
-
-	/* ensure outputs are set on failure */
-	*sortfunc = InvalidOid;
-	*issupport = false;
-	*reverse = false;
-	return false;
-}
-
 /*
  * get_equality_op_for_ordering_op
  *		Get the OID of the datatype-specific btree equality operator
diff --git a/src/backend/utils/sort/sortsupport.c b/src/backend/utils/sort/sortsupport.c
index 347f448e0f3..2240fd01001 100644
--- a/src/backend/utils/sort/sortsupport.c
+++ b/src/backend/utils/sort/sortsupport.c
@@ -18,6 +18,7 @@
 /* See sortsupport.h */
 #define SORTSUPPORT_INCLUDE_DEFINITIONS
 
+#include "access/nbtree.h"
 #include "fmgr.h"
 #include "utils/lsyscache.h"
 #include "utils/sortsupport.h"
@@ -94,24 +95,43 @@ PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup)
 void
 PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup)
 {
-	Oid			sortFunction;
-	bool		issupport;
+	Oid			sortSupportFunction;
+	Oid			opfamily;
+	Oid			opcintype;
+	int16		strategy;
 
-	if (!get_sort_function_for_ordering_op(orderingOp,
-										   &sortFunction,
-										   &issupport,
-										   &ssup->ssup_reverse))
+	Assert(ssup->comparator == NULL);
+
+	/* Find the operator in pg_amop */
+	if (!get_ordering_op_properties(orderingOp, &opfamily, &opcintype,
+									&strategy))
 		elog(ERROR, "operator %u is not a valid ordering operator",
 			 orderingOp);
+	ssup->ssup_reverse = (strategy == BTGreaterStrategyNumber);
 
-	if (issupport)
+	/* Look for a sort support function */
+	sortSupportFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
+											BTSORTSUPPORT_PROC);
+	if (OidIsValid(sortSupportFunction))
 	{
-		/* The sort support function should provide a comparator */
-		OidFunctionCall1(sortFunction, PointerGetDatum(ssup));
-		Assert(ssup->comparator != NULL);
+		/*
+		 * The sort support function can provide a comparator, but it can
+		 * also choose not to so (e.g. based on the selected collation).
+		 */
+		OidFunctionCall1(sortSupportFunction, PointerGetDatum(ssup));
 	}
-	else
+
+	if (ssup->comparator == NULL)
 	{
+		Oid			sortFunction;
+
+		sortFunction = get_opfamily_proc(opfamily, opcintype, opcintype,
+										 BTORDER_PROC);
+
+		if (!OidIsValid(sortFunction))
+			elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
+				 BTORDER_PROC, opcintype, opcintype, opfamily);
+
 		/* We'll use a shim to call the old-style btree comparator */
 		PrepareSortSupportComparisonShim(sortFunction, ssup);
 	}
diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index f46460a5757..07d24d4cb8a 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -50,8 +50,6 @@ extern Oid get_opfamily_member(Oid opfamily, Oid lefttype, Oid righttype,
 					int16 strategy);
 extern bool get_ordering_op_properties(Oid opno,
 						   Oid *opfamily, Oid *opcintype, int16 *strategy);
-extern bool get_sort_function_for_ordering_op(Oid opno, Oid *sortfunc,
-								  bool *issupport, bool *reverse);
 extern Oid	get_equality_op_for_ordering_op(Oid opno, bool *reverse);
 extern Oid	get_ordering_op_for_equality_op(Oid opno, bool use_lhs_type);
 extern List *get_mergejoin_opfamilies(Oid opno);