diff --git a/src/vim9compile.c b/src/vim9compile.c
index fb0adb3..a8a7647 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -5548,6 +5548,7 @@
     if (ufunc->uf_def_args.ga_len > 0)
     {
 	int	count = ufunc->uf_def_args.ga_len;
+	int	first_def_arg = ufunc->uf_args.ga_len - count;
 	int	i;
 	char_u	*arg;
 	int	off = STACK_FRAME_SIZE + (ufunc->uf_va_name != NULL ? 1 : 0);
@@ -5561,11 +5562,30 @@
 	    goto erret;
 	for (i = 0; i < count; ++i)
 	{
+	    garray_T	*stack = &cctx.ctx_type_stack;
+	    type_T	*val_type;
+	    int		arg_idx = first_def_arg + i;
+
 	    ufunc->uf_def_arg_idx[i] = instr->ga_len;
 	    arg = ((char_u **)(ufunc->uf_def_args.ga_data))[i];
-	    if (compile_expr1(&arg, &cctx) == FAIL
-		    || generate_STORE(&cctx, ISN_STORE,
-						i - count - off, NULL) == FAIL)
+	    if (compile_expr1(&arg, &cctx) == FAIL)
+		goto erret;
+
+	    // If no type specified use the type of the default value.
+	    // Otherwise check that the default value type matches the
+	    // specified type.
+	    val_type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+	    if (ufunc->uf_arg_types[arg_idx] == &t_unknown)
+		ufunc->uf_arg_types[arg_idx] = val_type;
+	    else if (check_type(ufunc->uf_arg_types[i], val_type, FALSE)
+								       == FAIL)
+	    {
+		arg_type_mismatch(ufunc->uf_arg_types[arg_idx], val_type,
+								  arg_idx + 1);
+		goto erret;
+	    }
+
+	    if (generate_STORE(&cctx, ISN_STORE, i - count - off, NULL) == FAIL)
 		goto erret;
 	}