diff --git a/include/internal/cpuid_x86.h b/include/internal/cpuid_x86.h
index 9dcee0d..754ca38 100644
--- a/include/internal/cpuid_x86.h
+++ b/include/internal/cpuid_x86.h
@@ -26,8 +26,7 @@ typedef struct {
   uint32_t eax, ebx, ecx, edx;
 } Leaf;
 
-// Retrieves the leaf for a particular cpuid.
-Leaf CpuId(uint32_t leaf_id);
+Leaf CpuIdEx(uint32_t leaf_id, int ecx);
 
 // Returns the eax value of the XCR0 register.
 uint32_t GetXCR0Eax(void);
diff --git a/src/cpuinfo_x86.c b/src/cpuinfo_x86.c
index 564f295..ea56c14 100644
--- a/src/cpuinfo_x86.c
+++ b/src/cpuinfo_x86.c
@@ -33,9 +33,9 @@
 
 #include <cpuid.h>
 
-Leaf CpuId(uint32_t leaf_id) {
+Leaf CpuIdEx(uint32_t leaf_id, int ecx) {
   Leaf leaf;
-  __cpuid_count(leaf_id, 0, leaf.eax, leaf.ebx, leaf.ecx, leaf.edx);
+  __cpuid_count(leaf_id, ecx, leaf.eax, leaf.ebx, leaf.ecx, leaf.edx);
   return leaf;
 }
 
@@ -53,10 +53,10 @@ uint32_t GetXCR0Eax(void) {
 #include <immintrin.h>
 #include <intrin.h>  // For __cpuidex()
 
-Leaf CpuId(uint32_t leaf_id) {
+Leaf CpuIdEx(uint32_t leaf_id, int ecx) {
   Leaf leaf;
   int data[4];
-  __cpuid(data, leaf_id);
+  __cpuidex(data, leaf_id, ecx);
   leaf.eax = data[0];
   leaf.ebx = data[1];
   leaf.ecx = data[2];
@@ -70,16 +70,24 @@ uint32_t GetXCR0Eax(void) { return _xgetbv(0); }
 #error "Unsupported compiler, x86 cpuid requires either GCC, Clang or MSVC."
 #endif
 
+static Leaf CpuId(uint32_t leaf_id) {
+  return CpuIdEx(leaf_id, 0);
+}
+
 static const Leaf kEmptyLeaf;
 
-static Leaf SafeCpuId(uint32_t max_cpuid_leaf, uint32_t leaf_id) {
+static Leaf SafeCpuIdEx(uint32_t max_cpuid_leaf, uint32_t leaf_id, int ecx) {
   if (leaf_id <= max_cpuid_leaf) {
-    return CpuId(leaf_id);
+    return CpuIdEx(leaf_id, ecx);
   } else {
     return kEmptyLeaf;
   }
 }
 
+static Leaf SafeCpuId(uint32_t max_cpuid_leaf, uint32_t leaf_id) {
+  return SafeCpuIdEx(max_cpuid_leaf, leaf_id, 0);
+}
+
 #define MASK_XMM 0x2
 #define MASK_YMM 0x4
 #define MASK_MASKREG 0x20
diff --git a/test/cpuinfo_x86_test.cc b/test/cpuinfo_x86_test.cc
index 2389de9..98d26c6 100644
--- a/test/cpuinfo_x86_test.cc
+++ b/test/cpuinfo_x86_test.cc
@@ -25,7 +25,7 @@ namespace cpu_features {
 
 class FakeCpu {
  public:
-  Leaf CpuId(uint32_t leaf_id) const {
+  Leaf CpuIdEx(uint32_t leaf_id, int ecx) const {
     const auto itr = cpuid_leaves_.find(leaf_id);
     EXPECT_TRUE(itr != cpuid_leaves_.end()) << "Missing leaf " << leaf_id;
     return itr->second;
@@ -48,7 +48,8 @@ class FakeCpu {
 
 auto* g_fake_cpu = new FakeCpu();
 
-extern "C" Leaf CpuId(uint32_t leaf_id) { return g_fake_cpu->CpuId(leaf_id); }
+extern "C" Leaf CpuIdEx(uint32_t leaf_id, int ecx) { return g_fake_cpu->CpuIdEx(leaf_id, ecx); }
+
 extern "C" uint32_t GetXCR0Eax(void) { return g_fake_cpu->GetXCR0Eax(); }
 
 namespace {