diff --git a/src/xenia/cpu/hir/hir_builder.cc b/src/xenia/cpu/hir/hir_builder.cc
index a27f0b86a..db278cd81 100644
--- a/src/xenia/cpu/hir/hir_builder.cc
+++ b/src/xenia/cpu/hir/hir_builder.cc
@@ -2074,6 +2074,17 @@ Value* HIRBuilder::AtomicExchange(Value* address, Value* new_value) {
   return i->dest;
 }
 
+Value* HIRBuilder::AtomicCompareExchange(Value* address, Value* old_value,
+                                         Value* new_value) {
+  ASSERT_ADDRESS_TYPE(address);
+  Instr* i = AppendInstr(OPCODE_ATOMIC_COMPARE_EXCHANGE_info, 0,
+                         AllocValue(INT8_TYPE));
+  i->set_src1(address);
+  i->set_src2(old_value);
+  i->set_src3(new_value);
+  return i->dest;
+}
+
 }  // namespace hir
 }  // namespace cpu
 }  // namespace xe
diff --git a/src/xenia/cpu/hir/hir_builder.h b/src/xenia/cpu/hir/hir_builder.h
index d6e0e8ccc..44a528f53 100644
--- a/src/xenia/cpu/hir/hir_builder.h
+++ b/src/xenia/cpu/hir/hir_builder.h
@@ -236,6 +236,8 @@ class HIRBuilder {
   Value* Unpack(Value* value, uint32_t pack_flags = 0);
 
   Value* AtomicExchange(Value* address, Value* new_value);
+  Value* AtomicCompareExchange(Value* address, Value* old_value,
+                               Value* new_value);
   Value* AtomicAdd(Value* address, Value* value);
   Value* AtomicSub(Value* address, Value* value);
 
diff --git a/src/xenia/cpu/hir/opcodes.h b/src/xenia/cpu/hir/opcodes.h
index 84bf2b320..8e440c73e 100644
--- a/src/xenia/cpu/hir/opcodes.h
+++ b/src/xenia/cpu/hir/opcodes.h
@@ -76,13 +76,14 @@ enum PackType : uint16_t {
   // Special types:
   PACK_TYPE_D3DCOLOR = 0,
   PACK_TYPE_FLOAT16_2 = 1,
-  PACK_TYPE_FLOAT16_4 = 2,
-  PACK_TYPE_SHORT_2 = 3,
-  PACK_TYPE_UINT_2101010 = 4,
+  PACK_TYPE_FLOAT16_3 = 2,  // FIXME: Not verified, but looks correct.
+  PACK_TYPE_FLOAT16_4 = 3,
+  PACK_TYPE_SHORT_2 = 4,
+  PACK_TYPE_UINT_2101010 = 5,
 
   // Types which use the bitmasks below for configuration:
-  PACK_TYPE_8_IN_16 = 5,
-  PACK_TYPE_16_IN_32 = 6,
+  PACK_TYPE_8_IN_16 = 6,
+  PACK_TYPE_16_IN_32 = 7,
 
   PACK_TYPE_MODE = 0x000F,  // just to get the mode
 
@@ -220,6 +221,7 @@ enum Opcode {
   OPCODE_PACK,
   OPCODE_UNPACK,
   OPCODE_ATOMIC_EXCHANGE,
+  OPCODE_ATOMIC_COMPARE_EXCHANGE,
   __OPCODE_MAX_VALUE,  // Keep at end.
 };
 
diff --git a/src/xenia/cpu/hir/opcodes.inl b/src/xenia/cpu/hir/opcodes.inl
index c5deb7ff8..a2968e238 100644
--- a/src/xenia/cpu/hir/opcodes.inl
+++ b/src/xenia/cpu/hir/opcodes.inl
@@ -631,3 +631,9 @@ DEFINE_OPCODE(
     "atomic_exchange",
     OPCODE_SIG_V_V_V,
     OPCODE_FLAG_VOLATILE)
+
+DEFINE_OPCODE(
+    OPCODE_ATOMIC_COMPARE_EXCHANGE,
+    "atomic_compare_exchange",
+    OPCODE_SIG_V_V_V_V,
+    OPCODE_FLAG_VOLATILE)