diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index c0ba087b40..6aca66f196 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -492,8 +492,16 @@ paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
 				return false;
 			}
 
-			*operators = lappend_oid(*operators, hasheqoperator);
-			*param_exprs = lappend(*param_exprs, expr);
+			/*
+			 * 'expr' may already exist as a parameter from a previous item in
+			 * ppi_clauses.  No need to include it again, however we'd better
+			 * ensure we do switch into binary mode if required.  See below.
+			 */
+			if (!list_member(*param_exprs, expr))
+			{
+				*operators = lappend_oid(*operators, hasheqoperator);
+				*param_exprs = lappend(*param_exprs, expr);
+			}
 
 			/*
 			 * When the join operator is not hashable then it's possible that
@@ -536,8 +544,16 @@ paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
 			return false;
 		}
 
-		*operators = lappend_oid(*operators, typentry->eq_opr);
-		*param_exprs = lappend(*param_exprs, expr);
+		/*
+		 * 'expr' may already exist as a parameter from the ppi_clauses.  No
+		 * need to include it again, however we'd better ensure we do switch
+		 * into binary mode.
+		 */
+		if (!list_member(*param_exprs, expr))
+		{
+			*operators = lappend_oid(*operators, typentry->eq_opr);
+			*param_exprs = lappend(*param_exprs, expr);
+		}
 
 		/*
 		 * We must go into binary mode as we don't have too much of an idea of
diff --git a/src/test/regress/expected/memoize.out b/src/test/regress/expected/memoize.out
index ca198ec3b8..17bb3c8661 100644
--- a/src/test/regress/expected/memoize.out
+++ b/src/test/regress/expected/memoize.out
@@ -107,7 +107,7 @@ WHERE t1.unique1 < 10;', false);
          ->  Index Scan using tenk1_unique1 on tenk1 t1 (actual rows=10 loops=N)
                Index Cond: (unique1 < 10)
          ->  Memoize (actual rows=2 loops=N)
-               Cache Key: t1.two, t1.two
+               Cache Key: t1.two
                Cache Mode: binary
                Hits: 8  Misses: 2  Evictions: Zero  Overflows: 0  Memory Usage: NkB
                ->  Subquery Scan on t2 (actual rows=2 loops=N)