diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index 661568c..3d97218 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -11,7 +11,7 @@ if(DOXYGEN_FOUND)
         COMMENT "Generating API documentation with Doxygen"
         VERBATIM)
 
-    install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/html DESTINATION ${CMAKE_INSTALL_DOCDIR})
+    install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/html DESTINATION ${CMAKE_INSTALL_DOCDIR} OPTIONAL)
 else()
     message(WARNING "Documentation enabled, but Doxygen cannot be found")
 endif()