diff --git a/FEXCore/Source/Interface/Core/CPUID.cpp b/FEXCore/Source/Interface/Core/CPUID.cpp
index d8e28181e..661b1f86c 100644
--- a/FEXCore/Source/Interface/Core/CPUID.cpp
+++ b/FEXCore/Source/Interface/Core/CPUID.cpp
@@ -14,6 +14,7 @@ $end_info$
 #include <FEXCore/Core/CPUID.h>
 #include <FEXCore/Core/HostFeatures.h>
 #include <FEXCore/Utils/FileLoading.h>
+#include <FEXCore/Utils/MathUtils.h>
 #include <FEXCore/fextl/string.h>
 #include <FEXHeaderUtils/Syscalls.h>
 
@@ -443,10 +444,10 @@ FEXCore::CPUID::FunctionResults CPUIDEmu::Function_01h(uint32_t Leaf) const {
 
   Res.eax = FAMILY_IDENTIFIER;
 
-  Res.ebx = 0 |             // Brand index
-            (8 << 8) |      // Cache line size in bytes
-            (Cores << 16) | // Number of addressable IDs for the logical cores in the physical CPU
-            (0 << 24);      // Local APIC ID
+  Res.ebx = 0 |                 // Brand index
+            (8 << 8) |          // Cache line size in bytes
+            (Cores << 16) |     // Number of addressable IDs for the logical cores in the physical CPU
+            (GetCPUID() << 24); // Local APIC ID
 
   Res.ecx = (1 << 0) |                                      // SSE3
             (CTX->HostFeatures.SupportsPMULL_128Bit << 1) | // PCLMULQDQ
@@ -509,7 +510,7 @@ FEXCore::CPUID::FunctionResults CPUIDEmu::Function_01h(uint32_t Leaf) const {
             (1 << 25) | // SSE
             (1 << 26) | // SSE2
             (0 << 27) | // Self Snoop
-            (1 << 28) | // Max APIC IDs reserved field is valid
+            (0 << 28) | // (HTT) Max APIC IDs reserved field is valid
             (1 << 29) | // Thermal monitor
             (0 << 30) | // Reserved
             (0 << 31);  // Pending break enable
@@ -1096,9 +1097,9 @@ FEXCore::CPUID::FunctionResults CPUIDEmu::Function_8000_0008h(uint32_t Leaf) con
             (CTX->HostFeatures.SupportsCLZERO << 0); // CLZERO support
 
   uint32_t CoreCount = Cores - 1;
-  Res.ecx = (0 << 16) |                                  // PerfTscSize: Performance timestamp count size
-            ((uint32_t)std::log2(CoreCount + 1) << 12) | // ApicIdSize: Number of bits in ApicID
-            (CoreCount << 0);                            // Count count subtract one
+  Res.ecx = (0 << 16) |                    // PerfTscSize: Performance timestamp count size
+            (std::bit_ceil(Cores) << 12) | // ApicIdSize: Number of bits in ApicID
+            (CoreCount << 0);              // Count count subtract one
 
   return Res;
 }
diff --git a/unittests/FEXLinuxTests/tests/cpu/cpu_count.cpp b/unittests/FEXLinuxTests/tests/cpu/cpu_count.cpp
new file mode 100644
index 000000000..89f219d0f
--- /dev/null
+++ b/unittests/FEXLinuxTests/tests/cpu/cpu_count.cpp
@@ -0,0 +1,104 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <cpuid.h>
+#include <optional>
+#include <unistd.h>
+#include <thread>
+
+TEST_CASE("cpu count - libraries") {
+  const auto hw_concurrency = std::thread::hardware_concurrency();
+  CHECK(hw_concurrency == sysconf(_SC_NPROCESSORS_CONF));
+  CHECK(hw_concurrency == sysconf(_SC_NPROCESSORS_ONLN));
+}
+
+struct core_info {
+  uint32_t local_apicid;
+  uint32_t max_addressible_ids;
+  uint32_t cores;
+  uint32_t threads;
+  bool HTT;
+};
+
+struct cpuid_fn {
+  uint32_t eax, ebx, ecx, edx;
+};
+
+cpuid_fn get_cpuid(uint32_t func, uint32_t leaf = 0) {
+  cpuid_fn fn {};
+  __cpuid_count(func, leaf, fn.eax, fn.ebx, fn.ecx, fn.edx);
+  return fn;
+}
+
+std::optional<core_info> cpuid_calculate_core_info() {
+  core_info info {};
+
+  // Legacy path
+  const auto cpuid_fn_0 = get_cpuid(0);
+  if (cpuid_fn_0.eax < 1) {
+    return std::nullopt;
+  }
+
+  const auto cpuid_fn_1 = get_cpuid(1);
+
+  info.local_apicid = cpuid_fn_1.ebx >> 24;
+  info.HTT = (cpuid_fn_1.edx >> 28) & 1;
+
+  const auto cpuid_fn_8000_0000 = get_cpuid(0x8000'0000U);
+
+  if (cpuid_fn_8000_0000.eax < 0x8000'0008) {
+    return std::nullopt;
+  }
+
+  const auto cpuid_fn_8000_0008 = get_cpuid(0x8000'0008U);
+  const uint32_t apic_id_size = (cpuid_fn_8000_0008.ecx >> 12) & 0xF;
+
+  // E.5.2: MNLP (Maximum Number of Logical Processors)
+  uint32_t MNLP {};
+
+  if (apic_id_size) {
+    // Extended topology.
+    MNLP = 1 << apic_id_size;
+  } else {
+    // Legacy path.
+    MNLP = (cpuid_fn_8000_0008.ecx & 0xF) + 1;
+  }
+
+  info.max_addressible_ids = MNLP;
+
+  const auto cpuid_fn_4 = get_cpuid(4);
+  if (cpuid_fn_4.eax & 0xF) {
+    // Intel exclusive cpuid function, AMD returns zero as unsupported.
+    // `Maximum number of addressable IDs for processor cores in the physical package`
+    info.cores = (cpuid_fn_4.eax >> 26) + 1;
+    if (info.HTT) {
+      // `A value of 1 for HTT indicates the value in CPUID.1.EBX[23:16] (the Maximum number of addressable IDs for logical processors in
+      // this package) is valid for the package. `Maximum number of addressable IDs for logical processors in this physical package`
+      info.threads = (cpuid_fn_1.ebx >> 16) & 0xFF;
+    } else {
+      info.threads = info.cores;
+    }
+  } else if (info.HTT) {
+    info.cores = (cpuid_fn_1.ebx >> 16) & 0xFF;
+    info.threads = info.cores * 2;
+  } else {
+    // Legacy path means cores/threads is equal to MNLP.
+    info.cores = info.threads = MNLP;
+  }
+
+  return info;
+}
+
+TEST_CASE("cpu count - cpuid") {
+  const auto hw_concurrency = std::thread::hardware_concurrency();
+  const auto core_info = cpuid_calculate_core_info();
+  REQUIRE(core_info.has_value());
+  CHECK(core_info->local_apicid < hw_concurrency);
+  CHECK(core_info->local_apicid < core_info->max_addressible_ids);
+  CHECK(core_info->max_addressible_ids >= hw_concurrency);
+  if (core_info->HTT) {
+    // May not be entirely correct on systems that mix HTT and non-HTT cpu cores.
+    CHECK((core_info->cores * 2) == core_info->threads);
+  } else {
+    CHECK(core_info->cores == core_info->threads);
+  }
+}