diff --git a/fastrpc/listener.c b/fastrpc/listener.c
index 10d3a46..d551ae9 100644
--- a/fastrpc/listener.c
+++ b/fastrpc/listener.c
@@ -19,6 +19,7 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <stddef.h>
 #include <stdio.h>
 
 #include "fastrpc.h"
@@ -29,6 +30,9 @@
 const struct fastrpc_interface *fastrpc_listener_interfaces[] = {
 };
 
+size_t fastrpc_listener_n_interfaces = sizeof(fastrpc_listener_interfaces)
+				     / sizeof(*fastrpc_listener_interfaces);
+
 static int adsp_listener_init2(int fd)
 {
 	return fastrpc2(&adsp_listener_init2_def, fd, ADSP_LISTENER_HANDLE);
@@ -192,8 +196,7 @@ static int invoke_requested_procedure(uint32_t handle,
 	uint8_t out_count;
 	int ret;
 
-	if (handle >= sizeof(fastrpc_listener_interfaces)
-		    / sizeof(*fastrpc_listener_interfaces)
+	if (handle >= fastrpc_listener_n_interfaces
 	 || REMOTE_SCALARS_METHOD(sc) >= fastrpc_listener_interfaces[handle]->n_procs)
 		return -1;
 
diff --git a/fastrpc/listener.h b/fastrpc/listener.h
index fef0379..c8262b5 100644
--- a/fastrpc/listener.h
+++ b/fastrpc/listener.h
@@ -1,6 +1,8 @@
 #ifndef LISTENER_H
 #define LISTENER_H
 
+#include <stddef.h>
+
 #include "fastrpc.h"
 #include "iobuffer.h"
 
@@ -17,6 +19,7 @@ struct fastrpc_interface {
 };
 
 extern const struct fastrpc_interface *fastrpc_listener_interfaces[];
+extern size_t fastrpc_listener_n_interfaces;
 
 int run_fastrpc_listener(int fd);