diff --git a/core/libs/prx/libSceAppContent/CMakeLists.txt b/core/libs/prx/libSceAppContent/CMakeLists.txt
new file mode 100644
index 000000000..ee3ad98c7
--- /dev/null
+++ b/core/libs/prx/libSceAppContent/CMakeLists.txt
@@ -0,0 +1,21 @@
+add_library(libSceAppContent SHARED EXCLUDE_FROM_ALL Export.cpp)
+target_include_directories(libSceAppContent PRIVATE ${LIBS_INCLUDE_DIR})
+configure_windows_unwind(libSceAppContent)
+
+if(MINGW)
+    foreach(runtimeLinkFlag IN ITEMS -static-libgcc -static-libstdc++ -static)
+        string(REPLACE "${runtimeLinkFlag}" "" CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}")
+    endforeach()
+endif()
+
+if(BUILD_TESTING)
+    add_test_executable(guest_appcontent_tests ${LIBS_INCLUDE_DIR}/tests/GuestAppContent.cpp)
+    target_include_directories(guest_appcontent_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_appcontent_tests PRIVATE libSceAppContent libc)
+    configure_windows_unwind(guest_appcontent_tests)
+    add_test(NAME guest_appcontent COMMAND guest_appcontent_tests)
+    if(WIN32)
+        set_tests_properties(guest_appcontent PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libSceAppContent>")
+    endif()
+endif()
diff --git a/core/libs/prx/libSceAppContent/Export.cpp b/core/libs/prx/libSceAppContent/Export.cpp
index 1d72d4913..dfc8300ad 100644
--- a/core/libs/prx/libSceAppContent/Export.cpp
+++ b/core/libs/prx/libSceAppContent/Export.cpp
@@ -10,6 +10,7 @@
 #include <string>
 
 static constexpr int SCE_APP_CONTENT_ERROR_PARAMETER = static_cast<int>(0x80D90002);
+static constexpr int SCE_APP_CONTENT_ERROR_NOT_FOUND = static_cast<int>(0x80D90005);
 static constexpr uint32_t APPPARAM_ID_SKU_FLAG = 1;
 static constexpr int32_t SKU_FLAG_FULL = 3;
 
@@ -30,16 +31,13 @@ extern "C" {
 
 int APS5_VABI sceAppContentAddcontMount(uint32_t service_label, const NpUnifiedEntitlementLabel* entitlement_label, AppContentMountPoint* mount_point) {
  (void)service_label;
- (void)entitlement_label;
- (void)mount_point;
- NotImplemented_nid_no_patch(__func__);
- return 0;
+ if (!entitlement_label || !mount_point) return SCE_APP_CONTENT_ERROR_PARAMETER;
+ return SCE_APP_CONTENT_ERROR_NOT_FOUND;
 }
 
 int APS5_VABI sceAppContentAddcontUnmount(const AppContentMountPoint* mount_point) {
- (void)mount_point;
- NotImplemented_nid_no_patch(__func__);
- return 0;
+ if (!mount_point) return SCE_APP_CONTENT_ERROR_PARAMETER;
+ return SCE_APP_CONTENT_ERROR_NOT_FOUND;
 }
 
 int APS5_VABI sceAppContentAppParamGetInt(uint32_t param_id, int32_t* value) {
diff --git a/core/libs/tests/GuestAppContent.cpp b/core/libs/tests/GuestAppContent.cpp
new file mode 100644
index 000000000..d78335075
--- /dev/null
+++ b/core/libs/tests/GuestAppContent.cpp
@@ -0,0 +1,27 @@
+#include "SceTypes.hpp"
+#include <cstdlib>
+#include <cstring>
+
+extern "C" {
+int APS5_VABI sceAppContentAddcontMount(uint32_t, const NpUnifiedEntitlementLabel*, AppContentMountPoint*);
+int APS5_VABI sceAppContentAddcontUnmount(const AppContentMountPoint*);
+}
+
+static constexpr int ErrorParameter = static_cast<int>(0x80D90002);
+static constexpr int ErrorNotFound = static_cast<int>(0x80D90005);
+static void Require(bool value) { if (!value) std::abort(); }
+
+int main() {
+    NpUnifiedEntitlementLabel label{};
+    std::memcpy(&label, "ADDCONT000000001", 16);
+    AppContentMountPoint mountPoint{};
+    std::memset(&mountPoint, 0x5a, sizeof(mountPoint));
+    const AppContentMountPoint untouched = mountPoint;
+    Require(sceAppContentAddcontMount(0, &label, &mountPoint) == ErrorNotFound);
+    Require(std::memcmp(&mountPoint, &untouched, sizeof(mountPoint)) == 0);
+    Require(sceAppContentAddcontMount(0, nullptr, &mountPoint) == ErrorParameter);
+    Require(sceAppContentAddcontMount(0, &label, nullptr) == ErrorParameter);
+    std::memcpy(mountPoint.data, "/addcont0", 10);
+    Require(sceAppContentAddcontUnmount(&mountPoint) == ErrorNotFound);
+    Require(sceAppContentAddcontUnmount(nullptr) == ErrorParameter);
+}
diff --git a/docs/dev/TechnicalDebt.md b/docs/dev/TechnicalDebt.md
index b57c3f774..7083e9275 100644
--- a/docs/dev/TechnicalDebt.md
+++ b/docs/dev/TechnicalDebt.md
@@ -120,6 +120,7 @@ Throughout the project, every function at every stage either **does exactly what
 
 ### Functional
 
+- [Additional content](../../core/libs/prx/libSceAppContent/Export.cpp) (libSceAppContent) is not installed or mounted: `sceAppContentAddcontMount` answers `NOT_FOUND` for every entitlement label and `sceAppContentAddcontUnmount` for every mount point, as no add-content mount is ever handed out
 - [libSceUlt queues](../../core/libs/prx/libSceUlt/Export.cpp) use preallocated host storage instead of the supplied guest work area; its existing size formula and the 512-byte object layouts remain unverified. Waiting-queue pool thread limits and waiter priority ordering are not implemented. Finalization wakes blocked queue callers with `ULT_ERROR_STATE`.
 - [MIMG `tfe` and `lwe`](../../core/shader/recompiler/RdnaDecoder/src/RdnaImageOpDecoder.cpp) never write the status VGPR after the data. On hardware it is written only when a texel fetch hits an unmapped page of a partially resident texture, or, for `lwe` on sample/gather, when the LOD is below the T# `MIN_LOD_WARN`; texture memory is always resident here, and `lwe` on sample, gather and `image_get_lod` throws.
 - [Image atomics](../../core/shader/recompiler/Optimization/src/ResourceMaterializer.cpp) on 32_SINT and 32_FLOAT surfaces act on the raw dword through an R32_UINT storage view; their float results are assumed to match those measured on 32_UINT surfaces. Other formats throw.