diff --git a/core/libs/prx/libkernel/AppMetadata/src/AppMetadata.cpp b/core/libs/prx/libkernel/AppMetadata/src/AppMetadata.cpp
index bc423779a..79df79827 100644
--- a/core/libs/prx/libkernel/AppMetadata/src/AppMetadata.cpp
+++ b/core/libs/prx/libkernel/AppMetadata/src/AppMetadata.cpp
@@ -42,6 +42,18 @@ void ensureTitleLoaded() {
     g_titleLoaded = true;
 }
 
+const bool g_downloadDataMounted = [] {
+    try {
+        const auto run = std::filesystem::current_path();
+        const auto paramJson = run / "app0" / "sce_sys" / "param.json";
+        if (!std::filesystem::exists(paramJson) || parseParamJson(paramJson).downloadDataSizeMiB == 0) return false;
+        std::filesystem::create_directories(run / "download0");
+        return true;
+    } catch (const std::exception&) {
+        return false;
+    }
+}();
+
 void ensureIconLoaded() {
     if (g_iconAttempted) return;
     g_iconAttempted = true;
diff --git a/core/libs/prx/libkernel/CMakeLists.txt b/core/libs/prx/libkernel/CMakeLists.txt
index b53d8a265..2ceb0cfa1 100644
--- a/core/libs/prx/libkernel/CMakeLists.txt
+++ b/core/libs/prx/libkernel/CMakeLists.txt
@@ -69,6 +69,29 @@ endif()
 configure_windows_unwind(libkernel)
 
 if(BUILD_TESTING)
+    add_test_executable(download_data_mount_tests ${LIBS_INCLUDE_DIR}/tests/GuestDownloadDataMount.cpp)
+    target_include_directories(download_data_mount_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(download_data_mount_tests PRIVATE libkernel libc)
+    configure_windows_unwind(download_data_mount_tests)
+    foreach(downloadDataCase IN ITEMS declared:256 none:0 invalid:256)
+        string(REPLACE ":" ";" downloadDataCase ${downloadDataCase})
+        list(GET downloadDataCase 0 downloadDataName)
+        list(GET downloadDataCase 1 downloadDataSize)
+        set(downloadDataRun ${CMAKE_CURRENT_BINARY_DIR}/download_data_mount_${downloadDataName})
+        if(downloadDataName STREQUAL "invalid")
+            file(WRITE ${downloadDataRun}/app0/sce_sys/param.json "{\"downloadDataSize\":${downloadDataSize}}")
+        else()
+            file(WRITE ${downloadDataRun}/app0/sce_sys/param.json
+                "{\"titleId\":\"PPSA00000\",\"localizedParameters\":{\"en-US\":{\"titleName\":\"Example\"}},\"downloadDataSize\":${downloadDataSize},"
+                "\"userDefinedParam1\":0,\"userDefinedParam2\":0,\"userDefinedParam3\":0,\"userDefinedParam4\":0}")
+        endif()
+        add_test(NAME download_data_mount_${downloadDataName} COMMAND download_data_mount_tests ${downloadDataName}
+            WORKING_DIRECTORY ${downloadDataRun})
+        if(WIN32)
+            set_tests_properties(download_data_mount_${downloadDataName} PROPERTIES ENVIRONMENT_MODIFICATION
+                "PATH=path_list_prepend:$<TARGET_FILE_DIR:libkernel>")
+        endif()
+    endforeach()
     add_test_executable(param_json_parser_tests ${LIBS_INCLUDE_DIR}/tests/ParamJsonParser.cpp)
     target_include_directories(param_json_parser_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(param_json_parser_tests PRIVATE libkernel libc)
diff --git a/core/libs/tests/GuestDownloadDataMount.cpp b/core/libs/tests/GuestDownloadDataMount.cpp
new file mode 100644
index 000000000..e588f786d
--- /dev/null
+++ b/core/libs/tests/GuestDownloadDataMount.cpp
@@ -0,0 +1,26 @@
+#include "prx/libkernel/AppMetadata/include/AppMetadata.hpp"
+#include <cstdlib>
+#include <cstring>
+#include <filesystem>
+#include <stdexcept>
+#include <string_view>
+
+static void Require(bool value) { if (!value) std::abort(); }
+
+int main(int argc, char** argv) {
+    Require(argc == 2);
+    const std::string_view mode = argv[1];
+    Require(std::filesystem::is_directory("download0") == (mode == "declared"));
+    if (mode == "invalid") {
+        bool rejected = false;
+        try {
+            GetAppTitleId_nid_postfix();
+        } catch (const std::runtime_error&) {
+            rejected = true;
+        }
+        Require(rejected);
+        return 0;
+    }
+    Require(std::strcmp(GetAppTitleId_nid_postfix().value, "PPSA00000") == 0);
+    std::filesystem::remove_all("download0");
+}