diff --git a/include/benchmark/benchmark.h b/include/benchmark/benchmark.h
index aef995e..7434a8a 100644
--- a/include/benchmark/benchmark.h
+++ b/include/benchmark/benchmark.h
@@ -241,6 +241,18 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
 #define BENCHMARK_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
 #endif
 
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+#if defined(__GNUC__) || __has_builtin(__builtin_unreachable)
+  #define BENCHMARK_UNREACHABLE() __builtin_unreachable()
+#elif defined(_MSC_VER)
+  #define BENCHMARK_UNREACHABLE() __assume(false)
+#else
+  #define BENCHMARK_UNREACHABLE() ((void)0)
+#endif
+
 namespace benchmark {
 class BenchmarkReporter;
 class MemoryManager;
@@ -1474,9 +1486,9 @@ inline const char* GetTimeUnitString(TimeUnit unit) {
     case kMicrosecond:
       return "us";
     case kNanosecond:
-    default:
       return "ns";
   }
+  BENCHMARK_UNREACHABLE();
 }
 
 inline double GetTimeUnitMultiplier(TimeUnit unit) {
@@ -1486,9 +1498,9 @@ inline double GetTimeUnitMultiplier(TimeUnit unit) {
     case kMicrosecond:
       return 1e6;
     case kNanosecond:
-    default:
       return 1e9;
   }
+  BENCHMARK_UNREACHABLE();
 }
 
 }  // namespace benchmark
diff --git a/src/internal_macros.h b/src/internal_macros.h
index b7e9203..32089e6 100644
--- a/src/internal_macros.h
+++ b/src/internal_macros.h
@@ -11,9 +11,6 @@
 #ifndef __has_feature
 #define __has_feature(x) 0
 #endif
-#ifndef __has_builtin
-#define __has_builtin(x) 0
-#endif
 
 #if defined(__clang__)
   #if !defined(COMPILER_CLANG)
@@ -87,14 +84,6 @@
   #define BENCHMARK_MAYBE_UNUSED
 #endif
 
-#if defined(COMPILER_GCC) || __has_builtin(__builtin_unreachable)
-  #define BENCHMARK_UNREACHABLE() __builtin_unreachable()
-#elif defined(COMPILER_MSVC)
-  #define BENCHMARK_UNREACHABLE() __assume(false)
-#else
-  #define BENCHMARK_UNREACHABLE() ((void)0)
-#endif
-
 // clang-format on
 
 #endif  // BENCHMARK_INTERNAL_MACROS_H_