diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 5d51f97f219..e3de67ace3a 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -23,6 +23,10 @@
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/selfuncs.h"
+#include "parser/parser.h"
+
+/* Hook for extensions to override OpExpr selectivity */
+opexpr_selectivity_hook_type opexpr_selectivity_hook = NULL;
 
 /*
  * Data structure for accumulating info about possible range-query
@@ -844,11 +848,21 @@ clause_selectivity_ext(PlannerInfo *root,
 		}
 		else
 		{
-			/* Estimate selectivity for a restriction clause. */
-			s1 = restriction_selectivity(root, opno,
-										 opclause->args,
-										 opclause->inputcollid,
-										 varRelid);
+			/*
+			 * Allow extensions to override OpExpr selectivity estimation
+			 * via the opexpr_selectivity_hook (Babelfish only).
+			 */
+			if (!(sql_dialect == SQL_DIALECT_TSQL &&
+				  opexpr_selectivity_hook &&
+				  opexpr_selectivity_hook(root, clause, varRelid, jointype,
+										  sjinfo, use_extended_stats, &s1)))
+			{
+				/* Estimate selectivity for a restriction clause. */
+				s1 = restriction_selectivity(root, opno,
+											 opclause->args,
+											 opclause->inputcollid,
+											 varRelid);
+			}
 		}
 
 		/*
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index c9ff71844e7..d42e13fdcf8 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -141,6 +141,10 @@
 #include "utils/syscache.h"
 #include "utils/timestamp.h"
 #include "utils/typcache.h"
+#include "parser/parser.h"
+
+/* Hook for extensions to override NullTest selectivity */
+nulltest_selectivity_hook_type nulltest_selectivity_hook = NULL;
 
 #define DEFAULT_PAGE_CPU_MULTIPLIER 50.0
 
@@ -1754,20 +1758,26 @@ nulltestsel(PlannerInfo *root, NullTestType nulltesttype, Node *arg,
 	else
 	{
 		/*
-		 * No ANALYZE stats available, so make a guess
+		 * No ANALYZE stats available. Allow extensions to override
+		 * NullTest selectivity via nulltest_selectivity_hook (Babelfish only).
 		 */
-		switch (nulltesttype)
+		if (!(sql_dialect == SQL_DIALECT_TSQL &&
+			  nulltest_selectivity_hook &&
+			  nulltest_selectivity_hook(root, nulltesttype, arg, varRelid, &selec)))
 		{
-			case IS_NULL:
-				selec = DEFAULT_UNK_SEL;
-				break;
-			case IS_NOT_NULL:
-				selec = DEFAULT_NOT_UNK_SEL;
-				break;
-			default:
-				elog(ERROR, "unrecognized nulltesttype: %d",
-					 (int) nulltesttype);
-				return (Selectivity) 0; /* keep compiler quiet */
+			switch (nulltesttype)
+			{
+				case IS_NULL:
+					selec = DEFAULT_UNK_SEL;
+					break;
+				case IS_NOT_NULL:
+					selec = DEFAULT_NOT_UNK_SEL;
+					break;
+				default:
+					elog(ERROR, "unrecognized nulltesttype: %d",
+						 (int) nulltesttype);
+					return (Selectivity) 0; /* keep compiler quiet */
+			}
 		}
 	}
 
diff --git a/src/include/utils/selfuncs.h b/src/include/utils/selfuncs.h
index fb4fa53363d..6632388d1e9 100644
--- a/src/include/utils/selfuncs.h
+++ b/src/include/utils/selfuncs.h
@@ -248,4 +248,21 @@ extern Selectivity scalararraysel_containment(PlannerInfo *root,
 											  Oid elemtype, bool isEquality, bool useOr,
 											  int varRelid);
 
+/* Babelfish hooks for selectivity estimation override */
+typedef bool (*opexpr_selectivity_hook_type) (PlannerInfo *root,
+											  Node *clause,
+											  int varRelid,
+											  JoinType jointype,
+											  SpecialJoinInfo *sjinfo,
+											  bool use_extended_stats,
+											  Selectivity *selec);
+extern PGDLLEXPORT opexpr_selectivity_hook_type opexpr_selectivity_hook;
+
+typedef bool (*nulltest_selectivity_hook_type) (PlannerInfo *root,
+											    NullTestType nulltesttype,
+											    Node *arg,
+											    int varRelid,
+											    Selectivity *selec);
+extern PGDLLEXPORT nulltest_selectivity_hook_type nulltest_selectivity_hook;
+
 #endif							/* SELFUNCS_H */