diff --git a/Python/ast_unparse.c b/Python/ast_unparse.c
index 5f366a1..f1b991a 100644
--- a/Python/ast_unparse.c
+++ b/Python/ast_unparse.c
@@ -193,22 +193,30 @@
 append_ast_args(_PyUnicodeWriter *writer, arguments_ty args)
 {
     bool first;
-    Py_ssize_t i, di, arg_count, default_count;
+    Py_ssize_t i, di, arg_count, posonlyarg_count, default_count;
 
     first = true;
 
-    /* positional arguments with defaults */
+    /* positional-only and positional arguments with defaults */
+    posonlyarg_count = asdl_seq_LEN(args->posonlyargs);
     arg_count = asdl_seq_LEN(args->args);
     default_count = asdl_seq_LEN(args->defaults);
-    for (i = 0; i < arg_count; i++) {
+    for (i = 0; i < posonlyarg_count + arg_count; i++) {
         APPEND_STR_IF_NOT_FIRST(", ");
-        APPEND(arg, (arg_ty)asdl_seq_GET(args->args, i));
+        if (i < posonlyarg_count){
+            APPEND(arg, (arg_ty)asdl_seq_GET(args->posonlyargs, i));
+        } else {
+            APPEND(arg, (arg_ty)asdl_seq_GET(args->args, i-posonlyarg_count));
+        }
 
-        di = i - arg_count + default_count;
+        di = i - posonlyarg_count - arg_count + default_count;
         if (di >= 0) {
             APPEND_STR("=");
             APPEND_EXPR((expr_ty)asdl_seq_GET(args->defaults, di), PR_TEST);
         }
+        if (posonlyarg_count && i + 1 == posonlyarg_count) {
+            APPEND_STR(", /");
+        }
     }
 
     /* vararg, or bare '*' if no varargs but keyword-only arguments present */
@@ -251,7 +259,9 @@
 append_ast_lambda(_PyUnicodeWriter *writer, expr_ty e, int level)
 {
     APPEND_STR_IF(level > PR_TEST, "(");
-    APPEND_STR(asdl_seq_LEN(e->v.Lambda.args->args) ? "lambda " : "lambda");
+    Py_ssize_t n_positional = (asdl_seq_LEN(e->v.Lambda.args->args) +
+                               asdl_seq_LEN(e->v.Lambda.args->posonlyargs));
+    APPEND_STR(n_positional ? "lambda " : "lambda");
     APPEND(args, e->v.Lambda.args);
     APPEND_STR(": ");
     APPEND_EXPR(e->v.Lambda.body, PR_TEST);