diff --git a/CMakeLists.txt b/CMakeLists.txt
index 802f71a..791f056 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -63,6 +63,7 @@
 set(SIZE32 int32_t)
 set(USIZE32 uint32_t)
 set(SIZE64 int64_t)
+set(USIZE64 uint64_t)
 
 configure_file(include/ogg/config_types.h.in ${CMAKE_CURRENT_BINARY_DIR}/include/ogg/config_types.h @ONLY)