Index: extern/CMakeLists.txt
--- extern/CMakeLists.txt.orig
+++ extern/CMakeLists.txt
@@ -159,13 +159,7 @@ 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/OpenMW/recastnavigation/archive/03259f3287ff8330f0d66fcd98d022edddffaa97.zip
-        URL_HASH SHA512=63db2ac90904764d7f1466d3c95994ec51d777cddd870b70f8ef674c09ed166b3d16ffc4ac1d18d0eab865fda4bf51b6ea17049025b66a338d3cadd0f48dc712
-        SOURCE_DIR fetched/recastnavigation
-    )
-    FetchContent_MakeAvailable(recastnavigation)
+    add_subdirectory("fetched/recastnavigation")
 endif()
 
 if (NOT OPENMW_USE_SYSTEM_SQLITE3)
