diff --git a/android/libass/src/main/cpp/CMakeLists.txt b/android/libass/src/main/cpp/CMakeLists.txt
index 261a5c45..d1017738 100644
--- a/android/libass/src/main/cpp/CMakeLists.txt
+++ b/android/libass/src/main/cpp/CMakeLists.txt
@@ -13,28 +13,39 @@ if(NOT DEFINED LIBASS_CACHE_DIR)
     set(LIBASS_CACHE_DIR "${CMAKE_BINARY_DIR}/libass-prebuilt")
 endif()
 set(LIBASS_ROOT "${LIBASS_CACHE_DIR}/libass-android-${LIBASS_VERSION}")
+set(LIBASS_ARCHIVE "${LIBASS_ROOT}/lib/${ANDROID_ABI}/libass.a")
+set(LIBASS_HEADER "${LIBASS_ROOT}/include/ass/ass.h")
 
-if(NOT EXISTS "${LIBASS_ROOT}/lib/${ANDROID_ABI}/libass.a")
-    set(_libass_zip "${LIBASS_CACHE_DIR}/libass-android-${LIBASS_VERSION}.zip")
-    message(STATUS "Fetching fork libass ${LIBASS_VERSION} from ${LIBASS_ZIP_URL}")
-    file(DOWNLOAD "${LIBASS_ZIP_URL}" "${_libass_zip}"
-        EXPECTED_HASH "SHA256=${LIBASS_SHA256}"
-        TLS_VERIFY ON
-        STATUS _libass_dl)
-    list(GET _libass_dl 0 _libass_dl_code)
-    if(NOT _libass_dl_code EQUAL 0)
-        file(REMOVE "${_libass_zip}")
-        message(FATAL_ERROR "Failed to download libass: ${_libass_dl}")
-    endif()
-    file(ARCHIVE_EXTRACT INPUT "${_libass_zip}" DESTINATION "${LIBASS_CACHE_DIR}")
-endif()
+# The downloaded archive lives under Flutter's root build/ directory, which can
+# be deleted without invalidating android/libass/.cxx. Model it as a Ninja output
+# so stale CMake configure caches can regenerate it during the build step.
+file(MAKE_DIRECTORY "${LIBASS_ROOT}/include")
+add_custom_command(
+    OUTPUT "${LIBASS_ARCHIVE}" "${LIBASS_HEADER}"
+    COMMAND "${CMAKE_COMMAND}"
+        "-DLIBASS_VERSION=${LIBASS_VERSION}"
+        "-DLIBASS_SHA256=${LIBASS_SHA256}"
+        "-DLIBASS_ZIP_URL=${LIBASS_ZIP_URL}"
+        "-DLIBASS_CACHE_DIR=${LIBASS_CACHE_DIR}"
+        "-DLIBASS_ROOT=${LIBASS_ROOT}"
+        "-DLIBASS_ARCHIVE=${LIBASS_ARCHIVE}"
+        "-DLIBASS_HEADER=${LIBASS_HEADER}"
+        "-DANDROID_ABI=${ANDROID_ABI}"
+        -P "${CMAKE_CURRENT_LIST_DIR}/FetchLibass.cmake"
+    COMMENT "Preparing fork libass ${LIBASS_VERSION} for ${ANDROID_ABI}"
+    VERBATIM)
+
+string(REPLACE "-" "_" LIBASS_ABI_TARGET "${ANDROID_ABI}")
+add_custom_target(libass_prebuilt_${LIBASS_ABI_TARGET}
+    DEPENDS "${LIBASS_ARCHIVE}" "${LIBASS_HEADER}")
 
 add_library(ass STATIC IMPORTED)
 set_target_properties(ass PROPERTIES
-    IMPORTED_LOCATION "${LIBASS_ROOT}/lib/${ANDROID_ABI}/libass.a")
+    IMPORTED_LOCATION "${LIBASS_ARCHIVE}")
 target_include_directories(ass INTERFACE "${LIBASS_ROOT}/include")
 
 add_library(${CMAKE_PROJECT_NAME} SHARED AssKt.c SurfaceTxProbe.c)
+add_dependencies(${CMAKE_PROJECT_NAME} libass_prebuilt_${LIBASS_ABI_TARGET})
 # HarfBuzz brings C++; link the shared STL that the app already packages.
 # (SurfaceTxProbe resolves its libandroid/libsync entry points via dlsym, so no extra link.)
 target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE
diff --git a/android/libass/src/main/cpp/FetchLibass.cmake b/android/libass/src/main/cpp/FetchLibass.cmake
new file mode 100644
index 00000000..14757602
--- /dev/null
+++ b/android/libass/src/main/cpp/FetchLibass.cmake
@@ -0,0 +1,47 @@
+cmake_minimum_required(VERSION 3.22.1)
+
+foreach(_var IN ITEMS
+        LIBASS_VERSION
+        LIBASS_SHA256
+        LIBASS_ZIP_URL
+        LIBASS_CACHE_DIR
+        LIBASS_ROOT
+        LIBASS_ARCHIVE
+        LIBASS_HEADER
+        ANDROID_ABI)
+    if(NOT DEFINED ${_var} OR "${${_var}}" STREQUAL "")
+        message(FATAL_ERROR "${_var} is required")
+    endif()
+endforeach()
+
+get_filename_component(_cache_parent "${LIBASS_CACHE_DIR}" DIRECTORY)
+file(MAKE_DIRECTORY "${_cache_parent}")
+
+# Android Gradle can build ABI variants in parallel; serialize the shared cache.
+file(LOCK "${LIBASS_CACHE_DIR}.lock" GUARD PROCESS TIMEOUT 300)
+
+if(NOT EXISTS "${LIBASS_ARCHIVE}" OR NOT EXISTS "${LIBASS_HEADER}")
+    file(MAKE_DIRECTORY "${LIBASS_CACHE_DIR}")
+    set(_libass_zip "${LIBASS_CACHE_DIR}/libass-android-${LIBASS_VERSION}.zip")
+
+    message(STATUS "Fetching fork libass ${LIBASS_VERSION} from ${LIBASS_ZIP_URL}")
+    file(DOWNLOAD "${LIBASS_ZIP_URL}" "${_libass_zip}"
+        EXPECTED_HASH "SHA256=${LIBASS_SHA256}"
+        TLS_VERIFY ON
+        STATUS _libass_dl)
+    list(GET _libass_dl 0 _libass_dl_code)
+    if(NOT _libass_dl_code EQUAL 0)
+        file(REMOVE "${_libass_zip}")
+        message(FATAL_ERROR "Failed to download libass: ${_libass_dl}")
+    endif()
+
+    file(REMOVE_RECURSE "${LIBASS_ROOT}")
+    file(ARCHIVE_EXTRACT INPUT "${_libass_zip}" DESTINATION "${LIBASS_CACHE_DIR}")
+endif()
+
+if(NOT EXISTS "${LIBASS_ARCHIVE}")
+    message(FATAL_ERROR "libass archive for ${ANDROID_ABI} was not extracted: ${LIBASS_ARCHIVE}")
+endif()
+if(NOT EXISTS "${LIBASS_HEADER}")
+    message(FATAL_ERROR "libass headers were not extracted: ${LIBASS_HEADER}")
+endif()