diff --git a/include/CMakeLists.txt b/include/CMakeLists.txt
index c0df415..5594349 100644
--- a/include/CMakeLists.txt
+++ b/include/CMakeLists.txt
@@ -1,5 +1,6 @@
 include(GNUInstallDirs)
 
-install(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
+# The trailing / is important.
+install(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/"
   DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}"
   FILES_MATCHING PATTERN "*.hpp")