diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 3a9f8d4da..86ee69087 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -4642,13 +4642,20 @@ dt_cg_subr_arg_to_tstring(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
 {
 	dt_ident_t	*idp;
 	dt_node_t	*arg = dnp->dn_args;
+	dt_idsig_t	*isp;
+	dt_node_t	*argtype;
 
 	TRACE_REGSET("    subr-arg_to_tstring:Begin");
 
+	assert(dnp->dn_ident && dnp->dn_ident);
+	isp = dnp->dn_ident->di_data;
+	assert(isp && isp->dis_args);
+	argtype = &isp->dis_args[0];
+
 	/* handle the one "input value" */
 	/* (its type matters only as to whether we check it is null */
 	dt_cg_node(arg, dlp, drp);
-	if (dt_node_is_pointer(arg) || dt_node_is_string(arg))
+	if (dt_node_is_pointer(argtype) || dt_node_is_string(argtype))
 		dt_cg_check_ptr_arg(dlp, drp, arg, NULL);
 
 	/* allocate the temporary string */
diff --git a/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6badaddr.d b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null.d
similarity index 100%
rename from test/unittest/funcs/inet_ntoa6/err.inet_ntoa6badaddr.d
rename to test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null.d
diff --git a/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null.r b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null.r
new file mode 100644
index 000000000..187543b63
--- /dev/null
+++ b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null.r
@@ -0,0 +1,3 @@
+
+-- @@stderr --
+dtrace: error on enabled probe ID 3 (ID 1: dtrace:::BEGIN): invalid address ({ptr}) in action #1 at BPF pc NNN
diff --git a/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.d b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.d
new file mode 100644
index 000000000..f5881d403
--- /dev/null
+++ b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.d
@@ -0,0 +1,19 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+#pragma D option quiet
+
+BEGIN
+{
+	inet_ntoa6(NULL);
+	exit(0);
+}
+
+ERROR
+{
+	exit(1);
+}
diff --git a/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.r b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.r
new file mode 100644
index 000000000..187543b63
--- /dev/null
+++ b/test/unittest/funcs/inet_ntoa6/err.inet_ntoa6.arg1_null_const.r
@@ -0,0 +1,3 @@
+
+-- @@stderr --
+dtrace: error on enabled probe ID 3 (ID 1: dtrace:::BEGIN): invalid address ({ptr}) in action #1 at BPF pc NNN