diff --git a/fastrpc/include/libhexagonrpc/interface.h b/fastrpc/include/libhexagonrpc/interface.h
new file mode 100644
index 0000000..e3eca4d
--- /dev/null
+++ b/fastrpc/include/libhexagonrpc/interface.h
@@ -0,0 +1,54 @@
+/*
+ * FastRPC interface method definition macros
+ *
+ * Copyright (C) 2023 Richard Acayan
+ *
+ * This file is part of sensh.
+ *
+ * Sensh is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef LIBHEXAGONRPC_INTERFACE_H
+#define LIBHEXAGONRPC_INTERFACE_H
+
+#include <libhexagonrpc/fastrpc.h>
+
+/*
+ * We want to declare method definitions as external by default so we only need
+ * special flags when compiling the interfaces. Otherwise, everything that uses
+ * the interfaces would need to define a macro.
+ */
+#if !HEXAGONRPC_BUILD_METHOD_DEFINITIONS
+
+#define HEXAGONRPC_DEFINE_REMOTE_METHOD(mid, name,			\
+					innums, inbufs,			\
+					outnums, outbufs)		\
+	extern const struct fastrpc_function_def_interp2 name##_def;
+
+#else /* HEXAGONRPC_BUILD_METHOD_DEFINITIONS */
+
+#define HEXAGONRPC_DEFINE_REMOTE_METHOD(mid, name,			\
+					innums, inbufs,			\
+					outnums, outbufs)		\
+	const struct fastrpc_function_def_interp2 name##_def = {	\
+		.msg_id = mid,						\
+		.in_nums = innums,					\
+		.in_bufs = inbufs,					\
+		.out_nums = outnums,					\
+		.out_bufs = outbufs,					\
+	};
+
+#endif /* HEXAGONRPC_BUILD_METHOD_DEFINITIONS */
+
+#endif /* LIBHEXAGONRPC_INTERFACE_H */