diff --git a/src/vim9compile.c b/src/vim9compile.c
index e5e3068..b005ff2 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -4416,6 +4416,12 @@
 
 	// "name" or "name()"
 	p = to_name_end(*arg, TRUE);
+	if (p - *arg == (size_t)1 && **arg == '_')
+	{
+	    emsg(_(e_cannot_use_underscore_here));
+	    return FAIL;
+	}
+
 	if (*p == '(')
 	{
 	    r = compile_call(arg, p - *arg, cctx, ppconst, 0);
@@ -6378,6 +6384,11 @@
 	    semsg(_(e_cannot_assign_to_constant), lhs.lhs_name);
 	    goto theend;
 	}
+	if (is_decl && lhs.lhs_name[0] == '_' && lhs.lhs_name[1] == NUL)
+	{
+	    emsg(_(e_cannot_use_underscore_here));
+	    goto theend;
+	}
 
 	if (!heredoc)
 	{