diff --git a/core/libs/prx/libSceAgc/DcbState/src/Init.cpp b/core/libs/prx/libSceAgc/DcbState/src/Init.cpp
index 7ad33c6d9..27f4ec973 100644
--- a/core/libs/prx/libSceAgc/DcbState/src/Init.cpp
+++ b/core/libs/prx/libSceAgc/DcbState/src/Init.cpp
@@ -7,6 +7,8 @@
 #include "SceTypes.hpp"
 #include "prx/libc/include/General.hpp"
 
+static constexpr int SCE_AGC_ERROR_INVALID_ARGUMENT = static_cast<int>(0x80890001);
+
 extern "C" {
 
 int APS5_VABI sceAgcInit_0090(std::uint32_t* state, std::uint32_t version) {
@@ -16,6 +18,7 @@ int APS5_VABI sceAgcInit_0090(std::uint32_t* state, std::uint32_t version) {
 }
 
 int APS5_VABI sceAgcInit(std::uint32_t version) {
+    if (version >= 14) return SCE_AGC_ERROR_INVALID_ARGUMENT;
     Agc::Command::GetRegisterDefaults(version, false, __func__);
     Agc::Command::GetRegisterDefaults(version, true, __func__);
     return 0;
diff --git a/core/libs/prx/libSceAgc/tests/Commands.cpp b/core/libs/prx/libSceAgc/tests/Commands.cpp
index e304b7fdc..03aeff906 100644
--- a/core/libs/prx/libSceAgc/tests/Commands.cpp
+++ b/core/libs/prx/libSceAgc/tests/Commands.cpp
@@ -50,6 +50,8 @@ extern "C" std::uint32_t* APS5_VABI sceAgcAcbAtomicGds_0900(CommandBuffer* buf,
 
 namespace {
 
+constexpr int SCE_AGC_ERROR_INVALID_ARGUMENT = static_cast<int>(0x80890001);
+
 void check(bool condition, const char* message) {
     if (!condition) {
         throw std::runtime_error(message);
@@ -622,8 +624,10 @@ void testDefaults() {
     expectFailure([] { sceAgcInit_0090(nullptr, 8); });
     expectFailure([&] { sceAgcInit_0090(&state, 14); });
     check(sceAgcInit(8) == 0, "AGC version initialization failed");
-    expectFailure([] { sceAgcInit(14); });
-    expectFailure([] { sceAgcInit(0xffffffffu); });
+    check(sceAgcInit(13) == 0, "AGC version 13 initialization failed");
+    check(sceAgcInit(14) == SCE_AGC_ERROR_INVALID_ARGUMENT, "unsupported AGC version did not return invalid argument");
+    check(sceAgcInit(0xffffffffu) == SCE_AGC_ERROR_INVALID_ARGUMENT, "maximum AGC version did not return invalid argument");
+    check(sceAgcInit(0xffffc278u) == SCE_AGC_ERROR_INVALID_ARGUMENT, "pointer-valued AGC argument did not return invalid argument");
     for (std::uint32_t version = 0; version < 14; ++version) {
         for (const bool internal : {false, true}) {
             auto* first = Agc::Command::GetRegisterDefaults(version, internal, __func__);
diff --git a/docs/dev/debt/libSceAgc.md b/docs/dev/debt/libSceAgc.md
index 0bbe3d5c1..fbddb208e 100644
--- a/docs/dev/debt/libSceAgc.md
+++ b/docs/dev/debt/libSceAgc.md
@@ -7,6 +7,7 @@
 - [sceAgcDcbSetCfRegisterDirect, sceAgcDcbSetCfRegisterRangeDirect](../../../core/libs/prx/libSceAgc/DcbState/src/Registers.cpp) (libSceAgc) - signatures follow [OpenAGC](https://github.com/OpenAGC/OpenAGC/blob/main/src/game_compat.c) and [SharpProspero](https://github.com/SvenGDK/SharpProspero/blob/main/src/SharpProspero/Interop/Agc/SceAgc.cs), which agree; the SET_CONFIG_REG (0x68) packet is OpenAGC's. The driver does not execute SET_CONFIG_REG, so a submitted packet throws
 - [Command buffer cursors](../../../core/libs/prx/libSceAgc/Command/src/Packet.cpp) (libSceAgc) - a null `cursor_down` is taken as a buffer without downward allocations, whose limit is `top`. PPSA16064 builds one-packet buffers of 8 dwords that way; the console's handling is unconfirmed
 - [sceAgcGetRegisterDefaultsInternal](../../../core/libs/prx/libSceAgc/Misc/src/RegisterDefaults.cpp) (libSceAgc) - returns the version 0 internal table, as `sceAgcGetRegisterDefaults` returns the version 0 public one; [OpenAGC](https://github.com/OpenAGC/OpenAGC/blob/main/src/game_compat.c) returns the table of the version passed to `sceAgcInit` instead, and null before it
+- [sceAgcInit](../../../core/libs/prx/libSceAgc/DcbState/src/Init.cpp) (libSceAgc) - unsupported register-default versions return `0x80890001` following [OpenAGC](https://github.com/OpenAGC/OpenAGC/blob/main/src/game_compat.c); AnyPS5 keeps version 13 support because its register-default tables include it, while that reference accepts only versions 0–12. The upper version accepted by PS5 firmware is unverified
 - [sceAgcSetSubmitMode](../../../core/libs/prx/libSceAgc/Misc/src/Suspend.cpp) (libSceAgc) - mode values unknown; only 0 is accepted
 - [sceAgcGetGsOversubscription](../../../core/libs/prx/libSceAgc/Shader/src/GsOversubscription.cpp) (libSceAgc) - signature and occupancy formula (base and expanded vertex/export capacities, budget shift, `GE_PC_ALLOC` / `SPI_SHADER_PGM_RSRC4_GS` encoding) follow KytyPS5 only, not confirmed on hardware or a title; a negative or NaN factor that gives a negative target, a missing GS context register or a zero `GE_MAX_OUTPUT_PER_SUBGROUP` throws
 - [sceAgcCbCondWrite](../../../core/libs/prx/libSceAgc/Cb/src/Branch.cpp) (libSceAgc) - argument order and the 9-dword COND_WRITE layout follow the clean-room [OpenAGC](https://github.com/OpenAGC/OpenAGC/blob/main/src/game_compat.c) and [sharpemu](https://github.com/sharpemu/sharpemu/blob/main/src/SharpEmu.Libs/Agc/AgcExports.CommandPackets.cs), which agree on them; SharpProspero lists another order. The write space is accepted only as 1 (memory), the one value both encode the same way, and other values throw.