diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index a4697dc..c530c4d 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -6157,7 +6157,7 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 	 * updates made so far by our own function.
 	 */
 	oldcontext = MemoryContextSwitchTo(get_eval_mcontext(estate));
-	if (!estate->readonly_func)
+	if (!estate->readonly_func && expr->expr_needs_snapshot)
 	{
 		CommandCounterIncrement();
 		PushActiveSnapshot(GetTransactionSnapshot());
@@ -6182,7 +6182,7 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 
 	estate->paramLI->parserSetupArg = save_setup_arg;
 
-	if (!estate->readonly_func)
+	if (!estate->readonly_func && expr->expr_needs_snapshot)
 		PopActiveSnapshot();
 
 	MemoryContextSwitchTo(oldcontext);
@@ -7978,6 +7978,43 @@ exec_simple_check_plan(PLpgSQL_execstate *estate, PLpgSQL_expr *expr)
 }
 
 /*
+ * expr_needs_snapshot --- check if expression contains calls of non-immutable functions or subqueries
+ */
+static bool
+expr_needs_snapshot(Node* expr, void* ctx)
+{
+	if (expr == NULL)
+		return false;
+	switch (nodeTag(expr))
+	{
+		case T_FuncExpr:
+		{
+			FuncExpr *func = (FuncExpr *)expr;
+			if (func_volatile(func->funcid) != PROVOLATILE_IMMUTABLE
+				|| !IsCatalogNamespace(get_func_namespace(func->funcid)))
+				return true;
+			break;
+		}
+		case T_OpExpr:
+		{
+			OpExpr *op = (OpExpr *)expr;
+			if (func_volatile(op->opfuncid) != PROVOLATILE_IMMUTABLE
+				|| !IsCatalogNamespace(get_func_namespace(op->opfuncid)))
+				return true;
+			break;
+		}
+		case T_Query:
+		case T_SubPlan:
+		case T_AlternativeSubPlan:
+		case T_SubLink:
+			return true;
+		default:
+			break;
+	}
+	return expression_tree_walker(expr, expr_needs_snapshot, ctx);
+}
+
+/*
  * exec_save_simple_expr --- extract simple expression from CachedPlan
  */
 static void
@@ -8046,6 +8083,7 @@ exec_save_simple_expr(PLpgSQL_expr *expr, CachedPlan *cplan)
 	 * current transaction".
 	 */
 	expr->expr_simple_expr = tle_expr;
+	expr->expr_needs_snapshot = expr_needs_snapshot(tle_expr, NULL);
 	expr->expr_simple_generation = cplan->generation;
 	expr->expr_simple_state = NULL;
 	expr->expr_simple_in_use = false;
diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index f66b2ba..454131f 100644
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -243,6 +243,7 @@ typedef struct PLpgSQL_expr
 	 */
 	ExprState  *expr_simple_state;	/* eval tree for expr_simple_expr */
 	bool		expr_simple_in_use; /* true if eval tree is active */
+	bool		expr_needs_snapshot; /* true if simple expression calls non-immutable functions or performs subqueries */
 	LocalTransactionId expr_simple_lxid;
 } PLpgSQL_expr;