diff --git a/highwayhash/arch_specific.cc b/highwayhash/arch_specific.cc
index 2a05860..314c84f 100644
--- a/highwayhash/arch_specific.cc
+++ b/highwayhash/arch_specific.cc
@@ -16,7 +16,7 @@
 
 #include <stdint.h>
 
-#if HH_ARCH_X64 && !HH_MSC_VERSION
+#if HH_ARCH_X86_X64 && !HH_MSC_VERSION
 #include <cpuid.h>
 #endif
 
@@ -53,7 +53,7 @@ const char* TargetName(const TargetBits target_bit) {
   }
 }
 
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
 
 namespace {
 
@@ -101,12 +101,12 @@ uint32_t ApicId() {
   return abcd[1] >> 24;  // ebx
 }
 
-#endif  // HH_ARCH_X64
+#endif  // HH_ARCH_X86_X64
 
 namespace {
 
 double DetectNominalClockRate() {
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
   const std::string& brand_string = BrandString();
   // Brand strings include the maximum configured frequency. These prefixes are
   // defined by Intel CPUID documentation.
diff --git a/highwayhash/arch_specific.h b/highwayhash/arch_specific.h
index 0b8c384..1cc35b5 100644
--- a/highwayhash/arch_specific.h
+++ b/highwayhash/arch_specific.h
@@ -52,6 +52,18 @@ namespace highwayhash {
 #define HH_ARCH_X64 0
 #endif
 
+#if defined(__i386__) || defined(_M_IX86)
+#define HH_ARCH_X86 1
+#else
+#define HH_ARCH_X86 0
+#endif
+
+#if HH_ARCH_X86 || HH_ARCH_X64
+#define HH_ARCH_X86_X64 1
+#else
+#define HH_ARCH_X86_X64 0
+#endif
+
 #if defined(__aarch64__) || defined(__arm64__)
 #define HH_ARCH_AARCH64 1
 #else
@@ -162,7 +174,7 @@ double NominalClockRate();
 // frequency on PPC and NominalClockRate on all other platforms.
 double InvariantTicksPerSecond();
 
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
 
 // Calls CPUID instruction with eax=level and ecx=count and returns the result
 // in abcd array where abcd = {eax, ebx, ecx, edx} (hence the name abcd).
@@ -172,7 +184,7 @@ void Cpuid(const uint32_t level, const uint32_t count,
 // Returns the APIC ID of the CPU on which we're currently running.
 uint32_t ApicId();
 
-#endif  // HH_ARCH_X64
+#endif  // HH_ARCH_X86_X64
 
 }  // namespace highwayhash
 
diff --git a/highwayhash/hh_avx2.h b/highwayhash/hh_avx2.h
index db44f53..4d76adb 100644
--- a/highwayhash/hh_avx2.h
+++ b/highwayhash/hh_avx2.h
@@ -78,7 +78,7 @@ def x(a,b,c):
     // size/32. mod32 is sufficient because each Update behaves as if a
     // counter were injected, because the state is large and mixed thoroughly.
     const V8x32U size256(
-        _mm256_broadcastd_epi32(_mm_cvtsi64_si128(size_mod32)));
+        _mm256_broadcastd_epi32(_mm_cvtsi32_si128(static_cast<uint32_t>(size_mod32))));
     // Equivalent to storing size_mod32 in packet.
     v0 += V4x64U(size256);
     // Boosts the avalanche effect of mod32.
@@ -105,12 +105,12 @@ def x(a,b,c):
     } else {  // size_mod32 < 16
       const V4x32U int_mask = IntMask<0>()(size);
       const V4x32U packetL = MaskedLoadInt(bytes, int_mask);
-      const uint64_t last3 =
+      const uint32_t last3 =
           Load3()(Load3::AllowUnordered(), remainder, size_mod4);
 
       // Rather than insert into packetL[3], it is faster to initialize
       // the otherwise empty packetH.
-      const V4x32U packetH(_mm_cvtsi64_si128(last3));
+      const V4x32U packetH(_mm_cvtsi32_si128(last3));
       Update(packetH, packetL);
     }
   }
@@ -255,7 +255,7 @@ def x(a,b,c):
   static HH_INLINE V4x32U Load0To16(const char* from, const size_t size_mod32,
                                     const V4x32U& size) {
     const char* remainder = from + (size_mod32 & ~3);
-    const uint64_t last3 = Load3()(Load3Policy(), remainder, size_mod32 & 3);
+    const uint32_t last3 = Load3()(Load3Policy(), remainder, size_mod32 & 3);
     const V4x32U int_mask = IntMask<kSizeOffset>()(size);
     const V4x32U int_lanes = MaskedLoadInt(from, int_mask);
     return Insert4AboveMask(last3, int_mask, int_lanes);
diff --git a/highwayhash/hh_portable.h b/highwayhash/hh_portable.h
index 3b1a394..628e1aa 100644
--- a/highwayhash/hh_portable.h
+++ b/highwayhash/hh_portable.h
@@ -233,7 +233,7 @@ class HHStatePortable {
     }
   }
 
-  static HH_INLINE void Rotate32By(uint32_t* halves, const uint64_t count) {
+  static HH_INLINE void Rotate32By(uint32_t* halves, const size_t count) {
     for (int i = 0; i < 2 * kNumLanes; ++i) {
       const uint32_t x = halves[i];
       halves[i] = (x << count) | (x >> (32 - count));
diff --git a/highwayhash/hh_sse41.h b/highwayhash/hh_sse41.h
index 6bbed22..7f71de8 100644
--- a/highwayhash/hh_sse41.h
+++ b/highwayhash/hh_sse41.h
@@ -97,12 +97,12 @@ class HHStateSSE41 {
     } else {  // size_mod32 < 16
       const V2x64U packetL = LoadMultipleOfFour(bytes, size_mod32);
 
-      const uint64_t last4 =
+      const uint32_t last4 =
           Load3()(Load3::AllowUnordered(), remainder, size_mod4);
 
       // Rather than insert into packetL[3], it is faster to initialize
       // the otherwise empty packetH.
-      const V2x64U packetH(_mm_cvtsi64_si128(last4));
+      const V2x64U packetH(_mm_cvtsi32_si128(last4));
       Update(packetH, packetL);
     }
   }
@@ -192,11 +192,11 @@ class HHStateSSE41 {
   // Rotates 32-bit lanes by "count" bits.
   static HH_INLINE void Rotate32By(V2x64U* HH_RESTRICT vH,
                                    V2x64U* HH_RESTRICT vL,
-                                   const uint64_t count) {
+                                   const size_t count) {
     // WARNING: the shift count is 64 bits, so we can't reuse vsize_mod32,
     // which is broadcast into 32-bit lanes.
-    const __m128i count_left = _mm_cvtsi64_si128(count);
-    const __m128i count_right = _mm_cvtsi64_si128(32 - count);
+    const __m128i count_left = _mm_cvtsi32_si128(static_cast<uint32_t>(count));
+    const __m128i count_right = _mm_cvtsi32_si128(static_cast<uint32_t>(32 - count));
     const V2x64U shifted_leftL(_mm_sll_epi32(*vL, count_left));
     const V2x64U shifted_leftH(_mm_sll_epi32(*vH, count_left));
     const V2x64U shifted_rightL(_mm_srl_epi32(*vL, count_right));
@@ -250,7 +250,7 @@ class HHStateSSE41 {
     const uint32_t* words = reinterpret_cast<const uint32_t*>(bytes);
     // Mask of 1-bits where the final 4 bytes should be inserted (replacement
     // for variable shift/insert using broadcast+blend).
-    V2x64U mask4(_mm_cvtsi64_si128(0xFFFFFFFFULL));  // 'insert' into lane 0
+    V2x64U mask4(_mm_cvtsi32_si128(0xFFFFFFFFU));  // 'insert' into lane 0
     V2x64U ret(0);
     if (size & 8) {
       ret = V2x64U(_mm_loadl_epi64(reinterpret_cast<const __m128i*>(words)));
diff --git a/highwayhash/highwayhash.h b/highwayhash/highwayhash.h
index 3655ce3..a9b18ab 100644
--- a/highwayhash/highwayhash.h
+++ b/highwayhash/highwayhash.h
@@ -31,7 +31,7 @@
 #include "highwayhash/compiler_specific.h"
 #include "highwayhash/hh_types.h"
 
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
 #include "highwayhash/iaca.h"
 #endif
 
diff --git a/highwayhash/highwayhash_target.cc b/highwayhash/highwayhash_target.cc
index 74022f6..34d4020 100644
--- a/highwayhash/highwayhash_target.cc
+++ b/highwayhash/highwayhash_target.cc
@@ -25,7 +25,7 @@ namespace highwayhash {
 extern "C" {
 uint64_t HH_ADD_TARGET_SUFFIX(HighwayHash64_)(const HHKey key,
                                               const char* bytes,
-                                              const uint64_t size) {
+                                              const size_t size) {
   HHStateT<HH_TARGET> state(key);
   HHResult64 result;
   HighwayHashT(&state, bytes, size, &result);
diff --git a/highwayhash/highwayhash_test.cc b/highwayhash/highwayhash_test.cc
index aed9a9e..60e4bae 100644
--- a/highwayhash/highwayhash_test.cc
+++ b/highwayhash/highwayhash_test.cc
@@ -79,7 +79,7 @@ TargetBits VerifyImplementations(const Result (&known_good)[kMaxSize + 1]) {
   // For each test input: empty string, 00, 00 01, ...
   char in[kMaxSize + 1] = {0};
   // Fast enough that we don't need a thread pool.
-  for (uint64_t size = 0; size <= kMaxSize; ++size) {
+  for (size_t size = 0; size <= kMaxSize; ++size) {
     in[size] = static_cast<char>(size);
 #if PRINT_RESULTS
     Result actual;
diff --git a/highwayhash/highwayhash_test_target.cc b/highwayhash/highwayhash_test_target.cc
index e999d9f..96af42e 100644
--- a/highwayhash/highwayhash_test_target.cc
+++ b/highwayhash/highwayhash_test_target.cc
@@ -127,7 +127,7 @@ void HighwayHashTest<Target>::operator()(const HHKey& key,
 template <TargetBits Target>
 void HighwayHashCatTest<Target>::operator()(const HHKey& key,
                                             const char* HH_RESTRICT bytes,
-                                            const uint64_t size,
+                                            const size_t size,
                                             const HHResult64* expected,
                                             const HHNotify notify) const {
   TestHighwayHashCat(key, bytes, size, expected, notify);
@@ -136,7 +136,7 @@ void HighwayHashCatTest<Target>::operator()(const HHKey& key,
 template <TargetBits Target>
 void HighwayHashCatTest<Target>::operator()(const HHKey& key,
                                             const char* HH_RESTRICT bytes,
-                                            const uint64_t size,
+                                            const size_t size,
                                             const HHResult128* expected,
                                             const HHNotify notify) const {
   TestHighwayHashCat(key, bytes, size, expected, notify);
@@ -145,7 +145,7 @@ void HighwayHashCatTest<Target>::operator()(const HHKey& key,
 template <TargetBits Target>
 void HighwayHashCatTest<Target>::operator()(const HHKey& key,
                                             const char* HH_RESTRICT bytes,
-                                            const uint64_t size,
+                                            const size_t size,
                                             const HHResult256* expected,
                                             const HHNotify notify) const {
   TestHighwayHashCat(key, bytes, size, expected, notify);
diff --git a/highwayhash/highwayhash_test_target.h b/highwayhash/highwayhash_test_target.h
index 56ae960..93be728 100644
--- a/highwayhash/highwayhash_test_target.h
+++ b/highwayhash/highwayhash_test_target.h
@@ -54,13 +54,13 @@ struct HighwayHashTest {
 template <TargetBits Target>
 struct HighwayHashCatTest {
   void operator()(const HHKey& key, const char* HH_RESTRICT bytes,
-                  const uint64_t size, const HHResult64* expected,
+                  const size_t size, const HHResult64* expected,
                   const HHNotify notify) const;
   void operator()(const HHKey& key, const char* HH_RESTRICT bytes,
-                  const uint64_t size, const HHResult128* expected,
+                  const size_t size, const HHResult128* expected,
                   const HHNotify notify) const;
   void operator()(const HHKey& key, const char* HH_RESTRICT bytes,
-                  const uint64_t size, const HHResult256* expected,
+                  const size_t size, const HHResult256* expected,
                   const HHNotify notify) const;
 };
 
diff --git a/highwayhash/instruction_sets.cc b/highwayhash/instruction_sets.cc
index a02e1f8..0aae595 100644
--- a/highwayhash/instruction_sets.cc
+++ b/highwayhash/instruction_sets.cc
@@ -17,7 +17,7 @@
 
 // Currently there are only specialized targets for X64; other architectures
 // only use HH_TARGET_Portable, in which case Supported() just returns that.
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
 
 #include <atomic>
 
@@ -138,4 +138,4 @@ TargetBits InstructionSets::Supported() {
 
 }  // namespace highwayhash
 
-#endif  // HH_ARCH_X64
+#endif  // HH_ARCH_X86_X64
diff --git a/highwayhash/instruction_sets.h b/highwayhash/instruction_sets.h
index aa7bd6b..756f561 100644
--- a/highwayhash/instruction_sets.h
+++ b/highwayhash/instruction_sets.h
@@ -34,7 +34,7 @@ class InstructionSets {
  public:
 // Returns bit array of HH_TARGET_* supported by the current CPU.
 // The HH_TARGET_Portable bit is guaranteed to be set.
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
   static TargetBits Supported();
 #elif HH_ARCH_PPC
   static HH_INLINE TargetBits Supported() {
@@ -54,7 +54,7 @@ class InstructionSets {
   // this should only be called infrequently (e.g. hoisting it out of loops).
   template <template <TargetBits> class Func, typename... Args>
   static HH_INLINE TargetBits Run(Args&&... args) {
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
     const TargetBits supported = Supported();
     if (supported & HH_TARGET_AVX2) {
       Func<HH_TARGET_AVX2>()(std::forward<Args>(args)...);
@@ -89,7 +89,7 @@ class InstructionSets {
   static HH_INLINE TargetBits RunAll(Args&&... args) {
     const TargetBits supported = Supported();
 
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
     if (supported & HH_TARGET_AVX2) {
       Func<HH_TARGET_AVX2>()(std::forward<Args>(args)...);
     }
diff --git a/highwayhash/load3.h b/highwayhash/load3.h
index 5e258e5..9d4d2a0 100644
--- a/highwayhash/load3.h
+++ b/highwayhash/load3.h
@@ -64,22 +64,22 @@ class Load3 {
   }
 
   // As above, but preceding bytes are removed and upper byte(s) are zero.
-  HH_INLINE uint64_t operator()(AllowReadBefore, const char* from,
+  HH_INLINE uint32_t operator()(AllowReadBefore, const char* from,
                                 const size_t size_mod4) {
     // Shift 0..3 valid bytes into LSB as if loaded in little-endian order.
     // 64-bit type enables 32-bit shift when size_mod4 == 0.
     uint64_t last3 = operator()(AllowReadBeforeAndReturn(), from, size_mod4);
     last3 >>= 32 - (size_mod4 * 8);
-    return last3;
+    return static_cast<uint32_t>(last3);
   }
 
   // The bytes need not be loaded in little-endian order. This particular order
   // (and the duplication of some bytes depending on "size_mod4") was chosen for
   // computational convenience and can no longer be changed because it is part
   // of the HighwayHash length padding definition.
-  HH_INLINE uint64_t operator()(AllowUnordered, const char* from,
+  HH_INLINE uint32_t operator()(AllowUnordered, const char* from,
                                 const size_t size_mod4) {
-    uint64_t last3 = 0;
+    uint32_t last3 = 0;
     // Not allowed to read any bytes; early-out is faster than reading from a
     // constant array of zeros.
     if (size_mod4 == 0) {
@@ -89,30 +89,30 @@ class Load3 {
     // These indices are chosen as an easy-to-compute sequence containing the
     // same elements as [0, size), but repeated and/or reordered. This enables
     // unconditional loads, which outperform conditional 8 or 16+8 bit loads.
-    const uint64_t idx0 = 0;
-    const uint64_t idx1 = size_mod4 >> 1;
-    const uint64_t idx2 = size_mod4 - 1;
+    const size_t idx0 = 0;
+    const size_t idx1 = size_mod4 >> 1;
+    const size_t idx2 = size_mod4 - 1;
     // Store into least significant bytes (avoids one shift).
-    last3 = U64FromChar(from[idx0]);
-    last3 += U64FromChar(from[idx1]) << 8;
-    last3 += U64FromChar(from[idx2]) << 16;
+    last3 = U32FromChar(from[idx0]);
+    last3 += U32FromChar(from[idx1]) << 8;
+    last3 += U32FromChar(from[idx2]) << 16;
     return last3;
   }
 
   // Must read exactly [0, size) bytes in little-endian order.
-  HH_INLINE uint64_t operator()(AllowNone, const char* from,
+  HH_INLINE uint32_t operator()(AllowNone, const char* from,
                                 const size_t size_mod4) {
     // We need to load in little-endian order without accessing anything outside
     // [from, from + size_mod4). Unrolling is faster than looping backwards.
-    uint64_t last3 = 0;
+    uint32_t last3 = 0;
     if (size_mod4 >= 1) {
-      last3 += U64FromChar(from[0]);
+      last3 += U32FromChar(from[0]);
     }
     if (size_mod4 >= 2) {
-      last3 += U64FromChar(from[1]) << 8;
+      last3 += U32FromChar(from[1]) << 8;
     }
     if (size_mod4 == 3) {
-      last3 += U64FromChar(from[2]) << 16;
+      last3 += U32FromChar(from[2]) << 16;
     }
     return last3;
   }
@@ -122,10 +122,6 @@ class Load3 {
     return static_cast<uint32_t>(static_cast<unsigned char>(c));
   }
 
-  static HH_INLINE uint64_t U64FromChar(const char c) {
-    return static_cast<uint64_t>(static_cast<unsigned char>(c));
-  }
-
   static HH_INLINE void Copy(const char* HH_RESTRICT from, const size_t size,
                              char* HH_RESTRICT to) {
 #if HH_MSC_VERSION
diff --git a/highwayhash/os_specific.cc b/highwayhash/os_specific.cc
index 0471043..1292135 100644
--- a/highwayhash/os_specific.cc
+++ b/highwayhash/os_specific.cc
@@ -249,7 +249,7 @@ void PinThreadToRandomCPU() {
 
   PinThreadToCPU(cpu);
 
-#if HH_ARCH_X64
+#if HH_ARCH_X86_X64
   // After setting affinity, we should be running on the desired CPU.
   printf("Running on CPU #%d, APIC ID %02x\n", cpu, ApicId());
 #else
diff --git a/highwayhash/tsc_timer.h b/highwayhash/tsc_timer.h
index e8119b5..654c76f 100644
--- a/highwayhash/tsc_timer.h
+++ b/highwayhash/tsc_timer.h
@@ -97,7 +97,7 @@ inline uint64_t Start<uint64_t>() {
   asm volatile("mfspr %0, %1" : "=r"(t) : "i"(268));
 #elif HH_ARCH_AARCH64
   asm volatile("mrs %0, cntvct_el0" : "=r"(t));
-#elif HH_ARCH_X64 && HH_MSC_VERSION
+#elif HH_ARCH_X32_X64 && HH_MSC_VERSION
   _mm_lfence();
   HH_COMPILER_FENCE;
   t = __rdtsc();
@@ -128,7 +128,7 @@ inline uint64_t Stop<uint64_t>() {
   asm volatile("mfspr %0, %1" : "=r"(t) : "i"(268));
 #elif HH_ARCH_AARCH64
   asm volatile("mrs %0, cntvct_el0" : "=r"(t));
-#elif HH_ARCH_X64 && HH_MSC_VERSION
+#elif HH_ARCH_X32_X64 && HH_MSC_VERSION
   HH_COMPILER_FENCE;
   unsigned aux;
   t = __rdtscp(&aux);
@@ -158,7 +158,7 @@ inline uint64_t Stop<uint64_t>() {
 template <>
 inline uint32_t Start<uint32_t>() {
   uint32_t t;
-#if HH_ARCH_X64 && HH_MSC_VERSION
+#if HH_ARCH_X32_X64 && HH_MSC_VERSION
   _mm_lfence();
   HH_COMPILER_FENCE;
   t = static_cast<uint32_t>(__rdtsc());
@@ -182,7 +182,7 @@ inline uint32_t Start<uint32_t>() {
 template <>
 inline uint32_t Stop<uint32_t>() {
   uint32_t t;
-#if HH_ARCH_X64 && HH_MSC_VERSION
+#if HH_ARCH_X32_X64 && HH_MSC_VERSION
   HH_COMPILER_FENCE;
   unsigned aux;
   t = static_cast<uint32_t>(__rdtscp(&aux));
diff --git a/highwayhash/vector256.h b/highwayhash/vector256.h
index d1ccec4..fcedb62 100644
--- a/highwayhash/vector256.h
+++ b/highwayhash/vector256.h
@@ -287,7 +287,14 @@ class V256<uint64_t> {
 
   // Broadcasts i to all lanes.
   HH_INLINE explicit V256(T i)
-      : v_(_mm256_broadcastq_epi64(_mm_cvtsi64_si128(i))) {}
+      : v_(_mm256_broadcastq_epi64(
+#if HH_ARCH_X86
+        // _mm_cvtsi64_si128 is not available on x86
+        _mm_insert_epi32(_mm_cvtsi32_si128(static_cast<uint32_t>(i)), static_cast<uint32_t>(i >> 32), 1)
+#else
+        _mm_cvtsi64_si128(i)
+#endif
+      )) {}
 
   // Copy from other vector.
   HH_INLINE explicit V256(const V256& other) : v_(other.v_) {}
@@ -536,7 +543,7 @@ HH_INLINE V256<T> operator&(const V256<T>& left, const V256<T>& right) {
 }
 
 template <typename T>
-HH_INLINE V256<T> operator|(const V256<T> left, const V256<T>& right) {
+HH_INLINE V256<T> operator|(const V256<T>& left, const V256<T>& right) {
   V256<T> t(left);
   return t |= right;
 }