diff --git a/ext/CMakeLists.txt b/ext/CMakeLists.txt
index 60df2d3bb441dc7b965d476a51dfef4d62abd234..78d6394cedffd5fea4399ca9c8ec6f8cd72591ec 100644
--- a/ext/CMakeLists.txt
+++ b/ext/CMakeLists.txt
@@ -60,6 +60,7 @@ function(add_external_cmake_project)
             # Add dummy DOWNLOAD_COMMAND to stop ExternalProject_Add terminating CMake if the
             # git submodule had not been udpated.
             DOWNLOAD_COMMAND "${CMAKE_COMMAND}" -E echo "Warning: ${EP_SOURCE_DIR} empty or missing."
+            BUILD_BYPRODUCTS "${EP_INTERFACE_LIB_NAME}"
             SOURCE_DIR "${EP_SOURCE_DIR}"
             CMAKE_ARGS "${EP_ALL_CMAKE_ARGS}"
             INSTALL_DIR "${EP_INSTALL_DIR}"