diff --git a/src/common/cityhash.cpp b/src/common/cityhash.cpp
index 84f044ed08..ab8db77746 100644
--- a/src/common/cityhash.cpp
+++ b/src/common/cityhash.cpp
@@ -42,6 +42,12 @@
 
 using namespace std;
 
+typedef uint8_t uint8;
+typedef uint32_t uint32;
+typedef uint64_t uint64;
+
+namespace Common {
+
 static uint64 UNALIGNED_LOAD64(const char* p) {
     uint64 result;
     memcpy(&result, p, sizeof(result));
@@ -648,3 +654,5 @@ uint128 CityHashCrc128(const char* s, size_t len) {
 }
 
 #endif
+
+} // namespace Common
diff --git a/src/common/cityhash.h b/src/common/cityhash.h
index 94499ce419..e6baf6a371 100644
--- a/src/common/cityhash.h
+++ b/src/common/cityhash.h
@@ -59,54 +59,55 @@
 // of a+b is easily derived from the hashes of a and b.  This property
 // doesn't hold for any hash functions in this file.
 
-#ifndef CITY_HASH_H_
-#define CITY_HASH_H_
+#pragma once
 
-#include <stdlib.h>  // for size_t.
-#include <stdint.h>
 #include <utility>
+#include <stdint.h>
+#include <stdlib.h> // for size_t.
 
-typedef uint8_t uint8;
-typedef uint32_t uint32;
-typedef uint64_t uint64;
-typedef std::pair<uint64, uint64> uint128;
+namespace Common {
 
-inline uint64 Uint128Low64(const uint128& x) { return x.first; }
-inline uint64 Uint128High64(const uint128& x) { return x.second; }
+typedef std::pair<uint64_t, uint64_t> uint128;
+
+inline uint64_t Uint128Low64(const uint128& x) {
+    return x.first;
+}
+inline uint64_t Uint128High64(const uint128& x) {
+    return x.second;
+}
 
 // Hash function for a byte array.
-uint64 CityHash64(const char *buf, size_t len);
+uint64_t CityHash64(const char* buf, size_t len);
 
 // Hash function for a byte array.  For convenience, a 64-bit seed is also
 // hashed into the result.
-uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);
+uint64_t CityHash64WithSeed(const char* buf, size_t len, uint64_t seed);
 
 // Hash function for a byte array.  For convenience, two seeds are also
 // hashed into the result.
-uint64 CityHash64WithSeeds(const char *buf, size_t len,
-                           uint64 seed0, uint64 seed1);
+uint64_t CityHash64WithSeeds(const char* buf, size_t len, uint64_t seed0, uint64_t seed1);
 
 // Hash function for a byte array.
-uint128 CityHash128(const char *s, size_t len);
+uint128 CityHash128(const char* s, size_t len);
 
 // Hash function for a byte array.  For convenience, a 128-bit seed is also
 // hashed into the result.
-uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);
+uint128 CityHash128WithSeed(const char* s, size_t len, uint128 seed);
 
 // Hash function for a byte array.  Most useful in 32-bit binaries.
-uint32 CityHash32(const char *buf, size_t len);
+uint32_t CityHash32(const char* buf, size_t len);
 
 // Hash 128 input bits down to 64 bits of output.
 // This is intended to be a reasonably good hash function.
-inline uint64 Hash128to64(const uint128& x) {
-  // Murmur-inspired hashing.
-  const uint64 kMul = 0x9ddfea08eb382d69ULL;
-  uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
-  a ^= (a >> 47);
-  uint64 b = (Uint128High64(x) ^ a) * kMul;
-  b ^= (b >> 47);
-  b *= kMul;
-  return b;
+inline uint64_t Hash128to64(const uint128& x) {
+    // Murmur-inspired hashing.
+    const uint64_t kMul = 0x9ddfea08eb382d69ULL;
+    uint64_t a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
+    a ^= (a >> 47);
+    uint64_t b = (Uint128High64(x) ^ a) * kMul;
+    b ^= (b >> 47);
+    b *= kMul;
+    return b;
 }
 
-#endif  // CITY_HASH_H_
+} // namespace Common