diff --git a/src/eval.c b/src/eval.c
index 5ec5b8a..c4d3781 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -263,9 +263,10 @@
 	if (partial->pt_func != NULL
 			  && partial->pt_func->uf_def_status != UF_NOT_COMPILED)
 	{
+	    // Shortcut to call a compiled function without overhead.
 	    // FIXME: should create a funccal and link it in current_funccal.
 	    if (call_def_function(partial->pt_func, argc, argv,
-						 partial, NULL, rettv) == FAIL)
+				DEF_USE_PT_ARGV, partial, NULL, rettv) == FAIL)
 		return FAIL;
 	}
 	else
diff --git a/src/proto/vim9execute.pro b/src/proto/vim9execute.pro
index bb3d414..b8360c5 100644
--- a/src/proto/vim9execute.pro
+++ b/src/proto/vim9execute.pro
@@ -15,7 +15,7 @@
 int may_break_in_function(ufunc_T *ufunc);
 int exe_typval_instr(typval_T *tv, typval_T *rettv);
 char_u *exe_substitute_instr(void);
-int call_def_function(ufunc_T *ufunc, int argc_arg, typval_T *argv, partial_T *partial, funccall_T *funccal, typval_T *rettv);
+int call_def_function(ufunc_T *ufunc, int argc_arg, typval_T *argv, int flags, partial_T *partial, funccall_T *funccal, typval_T *rettv);
 void unwind_def_callstack(ectx_T *ectx);
 void may_invoke_defer_funcs(ectx_T *ectx);
 void set_context_in_disassemble_cmd(expand_T *xp, char_u *arg);
diff --git a/src/testdir/test_user_func.vim b/src/testdir/test_user_func.vim
index ecf90b6..0a94264 100644
--- a/src/testdir/test_user_func.vim
+++ b/src/testdir/test_user_func.vim
@@ -635,6 +635,11 @@
   return val == 'c'
 enddef
 
+def DefIndexXtra(xtra: string, idx: number, val: string): bool
+  call writefile([idx .. ': ' .. val], 'Xentry' .. idx, 'D')
+  return val == 'c'
+enddef
+
 def Test_defer_in_funcref()
   assert_equal(2, indexof(['a', 'b', 'c'], function('g:FuncIndex')))
   assert_false(filereadable('Xentry0'))
@@ -655,6 +660,16 @@
   assert_false(filereadable('Xentry0'))
   assert_false(filereadable('Xentry1'))
   assert_false(filereadable('Xentry2'))
+
+  assert_equal(2, indexof(['a', 'b', 'c'], function(g:DefIndexXtra, ['xtra'])))
+  assert_false(filereadable('Xentry0'))
+  assert_false(filereadable('Xentry1'))
+  assert_false(filereadable('Xentry2'))
+
+  assert_equal(2, indexof(['a', 'b', 'c'], funcref(g:DefIndexXtra, ['xtra'])))
+  assert_false(filereadable('Xentry0'))
+  assert_false(filereadable('Xentry1'))
+  assert_false(filereadable('Xentry2'))
 enddef
 
 
diff --git a/src/userfunc.c b/src/userfunc.c
index 76ab6b9..1902778 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -2653,7 +2653,7 @@
 	    profile_may_start_func(&profile_info, fp, caller);
 #endif
 	sticky_cmdmod_flags = 0;
-	call_def_function(fp, argcount, argvars, funcexe->fe_partial,
+	call_def_function(fp, argcount, argvars, 0, funcexe->fe_partial,
 								    fc, rettv);
 	funcdepth_decrement();
 #ifdef FEAT_PROFILE
diff --git a/src/version.c b/src/version.c
index 36ce07e..ff5fd12 100644
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    405,
+/**/
     404,
 /**/
     403,
diff --git a/src/vim9.h b/src/vim9.h
index 22a3f39..9d72b96 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -759,3 +759,5 @@
 #define TVTT_DO_MEMBER	    1
 #define TVTT_MORE_SPECIFIC  2	// get most specific type for member
 
+// flags for call_def_function()
+#define DEF_USE_PT_ARGV	    1	// use the partial arguments
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 4625154..30ff7a7 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -5272,16 +5272,21 @@
     ufunc_T	*ufunc,
     int		argc_arg,	// nr of arguments
     typval_T	*argv,		// arguments
+    int		flags,		// DEF_ flags
     partial_T	*partial,	// optional partial for context
     funccall_T	*funccal,
     typval_T	*rettv)		// return value
 {
     ectx_T	ectx;		// execution context
     int		argc = argc_arg;
+    int		partial_argc = partial == NULL
+				  || (flags & DEF_USE_PT_ARGV) == 0
+							? 0 : partial->pt_argc;
+    int		total_argc = argc + partial_argc;
     typval_T	*tv;
     int		idx;
     int		ret = FAIL;
-    int		defcount = ufunc->uf_args.ga_len - argc;
+    int		defcount = ufunc->uf_args.ga_len - total_argc;
     sctx_T	save_current_sctx = current_sctx;
     int		did_emsg_before = did_emsg_cumul + did_emsg;
     int		save_suppress_errthrow = suppress_errthrow;
@@ -5345,14 +5350,14 @@
     ectx.ec_did_emsg_before = did_emsg_before;
     ++ex_nesting_level;
 
-    idx = argc - ufunc->uf_args.ga_len;
+    idx = total_argc - ufunc->uf_args.ga_len;
     if (idx > 0 && ufunc->uf_va_name == NULL)
     {
 	semsg(NGETTEXT(e_one_argument_too_many, e_nr_arguments_too_many,
-			idx), idx);
+								    idx), idx);
 	goto failed_early;
     }
-    idx = argc - ufunc->uf_args.ga_len + ufunc->uf_def_args.ga_len;
+    idx = total_argc - ufunc->uf_args.ga_len + ufunc->uf_def_args.ga_len;
     if (idx < 0)
     {
 	semsg(NGETTEXT(e_one_argument_too_few, e_nr_arguments_too_few,
@@ -5360,15 +5365,19 @@
 	goto failed_early;
     }
 
-    // Put arguments on the stack, but no more than what the function expects.
-    // A lambda can be called with more arguments than it uses.
-    for (idx = 0; idx < argc
+    // Put values from the partial and arguments on the stack, but no more than
+    // what the function expects.  A lambda can be called with more arguments
+    // than it uses.
+    for (idx = 0; idx < total_argc
 	    && (ufunc->uf_va_name != NULL || idx < ufunc->uf_args.ga_len);
 									 ++idx)
     {
+	int argv_idx = idx - partial_argc;
+
+	tv = idx < partial_argc ? partial->pt_argv + idx : argv + argv_idx;
 	if (idx >= ufunc->uf_args.ga_len - ufunc->uf_def_args.ga_len
-		&& argv[idx].v_type == VAR_SPECIAL
-		&& argv[idx].vval.v_number == VVAL_NONE)
+		&& tv->v_type == VAR_SPECIAL
+		&& tv->vval.v_number == VVAL_NONE)
 	{
 	    // Use the default value.
 	    STACK_TV_BOT(0)->v_type = VAR_UNKNOWN;
@@ -5377,10 +5386,10 @@
 	{
 	    if (ufunc->uf_arg_types != NULL && idx < ufunc->uf_args.ga_len
 		    && check_typval_arg_type(
-			ufunc->uf_arg_types[idx], &argv[idx],
-							NULL, idx + 1) == FAIL)
+			ufunc->uf_arg_types[idx], tv,
+						   NULL, argv_idx + 1) == FAIL)
 		goto failed_early;
-	    copy_tv(&argv[idx], STACK_TV_BOT(0));
+	    copy_tv(tv, STACK_TV_BOT(0));
 	}
 	++ectx.ec_stack.ga_len;
     }