diff --git a/core/libs/prx/libSceAjm.native/CMakeLists.txt b/core/libs/prx/libSceAjm.native/CMakeLists.txt
index a231a1529..0119f36b9 100644
--- a/core/libs/prx/libSceAjm.native/CMakeLists.txt
+++ b/core/libs/prx/libSceAjm.native/CMakeLists.txt
@@ -1,6 +1,9 @@
 enable_language(C)
 
 set(LIBATRAC9_DIR ${CMAKE_SOURCE_DIR}/3rdparty/LibAtrac9/C/src)
+set(LIBATRAC9_PATCHED_DIR ${CMAKE_CURRENT_BINARY_DIR}/atrac9)
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${LIBATRAC9_DIR}/unpack.c)
+include(${CMAKE_CURRENT_SOURCE_DIR}/PatchLibAtrac9.cmake)
 add_library(atrac9 STATIC EXCLUDE_FROM_ALL
         ${LIBATRAC9_DIR}/band_extension.c
         ${LIBATRAC9_DIR}/bit_allocation.c
@@ -13,9 +16,10 @@ add_library(atrac9 STATIC EXCLUDE_FROM_ALL
         ${LIBATRAC9_DIR}/quantization.c
         ${LIBATRAC9_DIR}/scale_factors.c
         ${LIBATRAC9_DIR}/tables.c
-        ${LIBATRAC9_DIR}/unpack.c
+        ${LIBATRAC9_PATCHED_DIR}/unpack.c
         ${LIBATRAC9_DIR}/utility.c
 )
+target_include_directories(atrac9 PRIVATE ${LIBATRAC9_DIR})
 set_target_properties(atrac9 PROPERTIES POSITION_INDEPENDENT_CODE ON)
 
 add_library(libSceAjm.native SHARED EXCLUDE_FROM_ALL
@@ -31,6 +35,16 @@ target_link_libraries(libSceAjm.native PRIVATE atrac9 ffmpeg libc libkernel)
 configure_windows_unwind(libSceAjm.native)
 
 if(BUILD_TESTING)
+    add_test_executable(atrac9_gradient_tests tests/Atrac9Gradient.c ${LIBATRAC9_DIR}/bit_reader.c)
+    target_include_directories(atrac9_gradient_tests PRIVATE ${LIBATRAC9_PATCHED_DIR} ${LIBATRAC9_DIR})
+    target_compile_options(atrac9_gradient_tests PRIVATE -ffunction-sections -fdata-sections)
+    if(APPLE)
+        target_link_options(atrac9_gradient_tests PRIVATE LINKER:-dead_strip)
+    else()
+        target_link_options(atrac9_gradient_tests PRIVATE LINKER:--gc-sections)
+    endif()
+    add_test(NAME atrac9_gradient COMMAND atrac9_gradient_tests)
+
     add_test_executable(guest_ajm_tests ${LIBS_INCLUDE_DIR}/tests/GuestAjm.cpp)
     target_include_directories(guest_ajm_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(guest_ajm_tests PRIVATE libSceAjm.native libc)
diff --git a/core/libs/prx/libSceAjm.native/PatchLibAtrac9.cmake b/core/libs/prx/libSceAjm.native/PatchLibAtrac9.cmake
new file mode 100644
index 000000000..e795b3fba
--- /dev/null
+++ b/core/libs/prx/libSceAjm.native/PatchLibAtrac9.cmake
@@ -0,0 +1,10 @@
+file(READ ${LIBATRAC9_DIR}/unpack.c libatrac9Unpack)
+set(libatrac9OldGuard "block->GradientEndUnit < 0 || block->GradientEndUnit >= 48")
+set(libatrac9NewGuard "block->GradientEndUnit < 0 || block->GradientEndUnit > 31")
+string(FIND "${libatrac9Unpack}" "${libatrac9OldGuard}" libatrac9GuardPosition)
+if(libatrac9GuardPosition EQUAL -1)
+    message(FATAL_ERROR "LibAtrac9 gradient guard has changed; review the local bounds fix")
+endif()
+string(REPLACE "${libatrac9OldGuard}" "${libatrac9NewGuard}" libatrac9Unpack "${libatrac9Unpack}")
+file(MAKE_DIRECTORY ${LIBATRAC9_PATCHED_DIR})
+file(WRITE ${LIBATRAC9_PATCHED_DIR}/unpack.c "${libatrac9Unpack}")
diff --git a/core/libs/prx/libSceAjm.native/tests/Atrac9Gradient.c b/core/libs/prx/libSceAjm.native/tests/Atrac9Gradient.c
new file mode 100644
index 000000000..5ad7595aa
--- /dev/null
+++ b/core/libs/prx/libSceAjm.native/tests/Atrac9Gradient.c
@@ -0,0 +1,36 @@
+#include "unpack.c"
+#include <stdlib.h>
+
+static void WriteBits(unsigned char* data, int* position, int value, int width)
+{
+    for (int bit = width - 1; bit >= 0; --bit)
+    {
+        int offset = (*position)++;
+        data[offset / 8] |= (unsigned char)(((value >> bit) & 1) << (7 - offset % 8));
+    }
+}
+
+static At9Status GradientStatus(int endUnit)
+{
+    unsigned char data[4] = {0};
+    int position = 0;
+    WriteBits(data, &position, 0, 2);
+    WriteBits(data, &position, 0, 6);
+    WriteBits(data, &position, endUnit - 1, 6);
+    WriteBits(data, &position, 0, 5);
+    WriteBits(data, &position, 0, 5);
+    WriteBits(data, &position, 0, 4);
+
+    Block block = {0};
+    BitReaderCxt reader;
+    InitBitReaderCxt(&reader, data, sizeof(data));
+    return ReadGradientParams(&block, &reader);
+}
+
+int main(void)
+{
+    if (GradientStatus(31) != ERR_SUCCESS) return EXIT_FAILURE;
+    if (GradientStatus(32) != ERR_UNPACK_GRAD_END_UNIT_OOB) return EXIT_FAILURE;
+    if (GradientStatus(47) != ERR_UNPACK_GRAD_END_UNIT_OOB) return EXIT_FAILURE;
+    return EXIT_SUCCESS;
+}