diff --git a/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/compute_unit.h b/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/compute_unit.h
index 26dbdd2eb0a..7a990c16f80 100644
--- a/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/compute_unit.h
+++ b/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/compute_unit.h
@@ -1339,7 +1339,8 @@ class RJ_API_TYPE_EXPORT ComputeUnitCore : public simdojo::CompositeComponent {
   /// `UnimplementedInst::what()` when that legacy exception is translated.
   /// Otherwise the pointed-to string is unchanged.
   /// @returns Failure for an unimplemented instruction stub or a reported operand
-  /// failure. The wavefront retains the reason for caller-owned diagnostics.
+  /// or register-access failure. The wavefront retains the reason for caller-owned
+  /// diagnostics.
   /// Each call clears the previous error; a failed call does not halt the wavefront.
   /// Other host failures inside implemented instructions still raise exceptions.
   util::Result execute_instruction(Instruction *inst, Wavefront &wf,
diff --git a/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/register_access.h b/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/register_access.h
index b8eb013a54d..7d21d460b0b 100644
--- a/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/register_access.h
+++ b/emulation/rocjitsu/lib/rocjitsu/src/rocjitsu/vm/amdgpu/register_access.h
@@ -806,6 +806,9 @@ class RegisterAccess {
       });
     }
 
+    /// @brief Return raw lane words for one register in the region.
+    /// @returns Failure for a partial-byte region, reporting InvalidRegisterAccess
+    /// through the wavefront's instruction-execution error channel.
     FailureOr<std::span<const uint32_t>> lanes(uint32_t relative_reg = 0) const {
       assert(relative_reg < reg_count_ && "relative VGPR outside read region");
       if (byte_mask_ != rocjitsu::ExecutionPlugin::kFullByteMask)
diff --git a/emulation/rocjitsu/tests/register_access_test.cpp b/emulation/rocjitsu/tests/register_access_test.cpp
index 9aa6a6bde03..005683bf13a 100644
--- a/emulation/rocjitsu/tests/register_access_test.cpp
+++ b/emulation/rocjitsu/tests/register_access_test.cpp
@@ -1883,6 +1883,29 @@ TEST(RegisterAccessTest, PartialByteRawRegionOperationsRejectBeforeSideEffects)
   expect_failure([&] { return region.copy_dwords_lane_major(bytes, 1); });
 }
 
+TEST(RegisterAccessTest, OversizedRawRegionCopyRejectsBeforeSideEffects) {
+  Fixture fx(ROCJITSU_CODE_ARCH_CDNA4, kSgprsPerWave, /*wavefront_slots=*/1, kVgprsPerWave,
+             /*wave_size=*/64);
+  ASSERT_NE(fx.wf, nullptr);
+  ASSERT_EQ(fx.wf->wf_size(), 64u);
+  for (uint32_t lane = 0; lane < fx.wf->wf_size(); ++lane)
+    fx.cu->write_vgpr(fx.vgpr_base(), lane, 0x12340000u + lane);
+  auto region = RegisterAccess(*fx.wf).read_vgpr_region(
+      fx.vgpr_base(), /*reg_count=*/1, /*lane_mask=*/~uint64_t{0}, ExecutionPlugin::kFullByteMask);
+  ASSERT_TRUE(region.valid());
+  std::array<uint32_t, 65> words;
+  words.fill(0xAABBCCDDu);
+  const auto original_words = words;
+
+  fx.wf->clear_instruction_execution_error();
+  ASSERT_EQ(fx.wf->instruction_execution_error(), InstructionExecutionError::None);
+  ASSERT_EQ(fx.wf->instruction_execution_error_detail(), nullptr);
+  EXPECT_TRUE(region.copy_to(words).failed());
+  EXPECT_EQ(fx.wf->instruction_execution_error(), InstructionExecutionError::InvalidRegisterAccess);
+  EXPECT_STREQ(fx.wf->instruction_execution_error_detail(), "destination exceeds read region");
+  EXPECT_EQ(words, original_words);
+}
+
 TEST(RegisterAccessTest, ScalarBackedPartialByteStoresRejectBeforeObservation) {
   Fixture fx;
   ASSERT_NE(fx.wf, nullptr);