diff --git a/third-party/mcrouter/src/mcrouter/flavor.cpp b/third-party/mcrouter/src/mcrouter/flavor.cpp
index e60dc701a50675..a3bdf176f162b2 100644
--- a/third-party/mcrouter/src/mcrouter/flavor.cpp
+++ b/third-party/mcrouter/src/mcrouter/flavor.cpp
@@ -20,9 +20,7 @@
 
 #include "mcrouter/lib/fbi/cpp/util.h"
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 namespace {
 
@@ -170,6 +168,4 @@ bool parse_json_options(
 
   return true;
 }
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/flavor.h b/third-party/mcrouter/src/mcrouter/flavor.h
index 27419cfd692b28..847000762bf775 100644
--- a/third-party/mcrouter/src/mcrouter/flavor.h
+++ b/third-party/mcrouter/src/mcrouter/flavor.h
@@ -14,9 +14,7 @@ namespace folly {
 struct dynamic;
 } // namespace folly
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 /**
  * Reads mcrouter flavor file and fills the given dictionaries.
@@ -52,6 +50,4 @@ bool parse_json_options(
     const folly::dynamic& json,
     const std::string& field_name,
     std::unordered_map<std::string, std::string>& opts);
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.cpp b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.cpp
index d8a530449165df..072219ff7eab99 100644
--- a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.cpp
+++ b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.cpp
@@ -8,9 +8,7 @@
 #include "AuxiliaryCPUThreadPool.h"
 #include <folly/Singleton.h>
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 // Number of CPU threads to run in CPU thread pool.
 constexpr size_t kNumCPUThreads = 5;
@@ -29,6 +27,4 @@ folly::CPUThreadPoolExecutor& AuxiliaryCPUThreadPool::getThreadPool() {
   return *threadPool_;
 }
 
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.h b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.h
index 67993fd15a39a8..05b75c4cedb3e1 100644
--- a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.h
+++ b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryCPUThreadPool.h
@@ -11,9 +11,7 @@
 #include <folly/executors/CPUThreadPoolExecutor.h>
 #include <folly/synchronization/CallOnce.h>
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 /**
  * CPU Thread pool that is shared between router intances.
@@ -33,6 +31,4 @@ class AuxiliaryCPUThreadPool {
 using AuxiliaryCPUThreadPoolSingleton =
     folly::Singleton<AuxiliaryCPUThreadPool>;
 
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.cpp b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.cpp
index 6cdbee26362060..14b7643ab9a952 100644
--- a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.cpp
+++ b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.cpp
@@ -8,9 +8,7 @@
 #include "AuxiliaryIOThreadPool.h"
 #include <folly/Singleton.h>
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 // Number of IO threads to run in IO thread pool.
 constexpr size_t kNumIOThreads = 5;
@@ -29,6 +27,4 @@ folly::IOThreadPoolExecutorBase& AuxiliaryIOThreadPool::getThreadPool() {
   return *threadPool_;
 }
 
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.h b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.h
index d6e9063e1c21e3..8c83bce20ade3a 100644
--- a/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.h
+++ b/third-party/mcrouter/src/mcrouter/lib/AuxiliaryIOThreadPool.h
@@ -11,9 +11,7 @@
 #include <folly/executors/IOThreadPoolExecutor.h>
 #include <folly/synchronization/CallOnce.h>
 
-namespace facebook {
-namespace memcache {
-namespace mcrouter {
+namespace facebook::memcache::mcrouter {
 
 /**
  * IO Thread pool that is shared between router intances.
@@ -32,6 +30,4 @@ class AuxiliaryIOThreadPool {
 
 using AuxiliaryIOThreadPoolSingleton = folly::Singleton<AuxiliaryIOThreadPool>;
 
-} // namespace mcrouter
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::mcrouter
diff --git a/third-party/mcrouter/src/mcrouter/lib/CacheClientStats.h b/third-party/mcrouter/src/mcrouter/lib/CacheClientStats.h
index 51abad2fcfd0e2..567461495e1182 100644
--- a/third-party/mcrouter/src/mcrouter/lib/CacheClientStats.h
+++ b/third-party/mcrouter/src/mcrouter/lib/CacheClientStats.h
@@ -10,8 +10,7 @@
 #include <folly/SpinLock.h>
 #include <folly/concurrency/CacheLocality.h>
 
-namespace facebook {
-namespace memcache {
+namespace facebook::memcache {
 
 struct CacheClientCounters {
   size_t fetchCount{0};
@@ -69,5 +68,4 @@ class CacheClientStats {
       lock_;
   CacheClientCounters counters_;
 };
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache
diff --git a/third-party/mcrouter/src/mcrouter/lib/Ch3HashFunc.h b/third-party/mcrouter/src/mcrouter/lib/Ch3HashFunc.h
index c86ee0527092b6..372686c6b7bae0 100644
--- a/third-party/mcrouter/src/mcrouter/lib/Ch3HashFunc.h
+++ b/third-party/mcrouter/src/mcrouter/lib/Ch3HashFunc.h
@@ -16,8 +16,7 @@ namespace folly {
 struct dynamic;
 } // namespace folly
 
-namespace facebook {
-namespace memcache {
+namespace facebook::memcache {
 
 /* CH3 consistent hashing function object */
 class Ch3HashFunc {
@@ -43,5 +42,4 @@ class Ch3HashFunc {
  private:
   size_t n_;
 };
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache
diff --git a/third-party/mcrouter/src/mcrouter/lib/Clocks.cpp b/third-party/mcrouter/src/mcrouter/lib/Clocks.cpp
index 16db6e6e901413..daa1dd8dd75e78 100644
--- a/third-party/mcrouter/src/mcrouter/lib/Clocks.cpp
+++ b/third-party/mcrouter/src/mcrouter/lib/Clocks.cpp
@@ -8,9 +8,7 @@
 #include "Clocks.h"
 #include <sys/time.h>
 
-namespace facebook {
-namespace memcache {
-namespace cycles {
+namespace facebook::memcache::cycles {
 
 uint64_t getCpuCycles() noexcept {
 #if defined(__x86_64__)
@@ -53,6 +51,4 @@ uint64_t getCpuCycles() noexcept {
 #endif
 }
 
-} // namespace cycles
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::cycles
diff --git a/third-party/mcrouter/src/mcrouter/lib/Clocks.h b/third-party/mcrouter/src/mcrouter/lib/Clocks.h
index 0a6f5c56e95a44..c1172e0bd22ffc 100644
--- a/third-party/mcrouter/src/mcrouter/lib/Clocks.h
+++ b/third-party/mcrouter/src/mcrouter/lib/Clocks.h
@@ -9,9 +9,7 @@
 
 #include <cstdint>
 
-namespace facebook {
-namespace memcache {
-namespace cycles {
+namespace facebook::memcache::cycles {
 
 /**
  * Returns the number of cpu cycles since power-on. This clock doesn't involve
@@ -25,6 +23,4 @@ namespace cycles {
  */
 uint64_t getCpuCycles() noexcept;
 
-} // namespace cycles
-} // namespace memcache
-} // namespace facebook
+} // namespace facebook::memcache::cycles