Index: extern/CMakeLists.txt
--- extern/CMakeLists.txt.orig
+++ extern/CMakeLists.txt
@@ -173,13 +173,7 @@ if(NOT OPENMW_USE_SYSTEM_RECASTNAVIGATION)
     set(RECASTNAVIGATION_TESTS OFF CACHE BOOL "")
     set(RECASTNAVIGATION_EXAMPLES OFF CACHE BOOL "")
 
-    include(FetchContent)
-    FetchContent_Declare(recastnavigation
-        URL https://github.com/recastnavigation/recastnavigation/archive/c393777d26d2ff6519ac23612abf8af42678c9dd.zip
-        URL_HASH SHA512=48f20cee7a70c2f20f4c68bb74d5af11a1434be85294e37f5fe7b7aae820fbcdff4f35d3be286eaf6f9cbce0aed4201fcc090df409a5bd04aec5fd7c29b3ad94
-        SOURCE_DIR fetched/recastnavigation
-    )
-    FetchContent_MakeAvailableExcludeFromAll(recastnavigation)
+    add_subdirectory("fetched/recastnavigation")
 endif()
 
 if (NOT OPENMW_USE_SYSTEM_SQLITE3)
