diff --git a/include/gsl/assert b/include/gsl/assert
index 08f7a5e..6cca337 100644
--- a/include/gsl/assert
+++ b/include/gsl/assert
@@ -57,20 +57,6 @@
 #define GSL_STRINGIFY_DETAIL(x) #x
 #define GSL_STRINGIFY(x) GSL_STRINGIFY_DETAIL(x)
 
-//
-// GSL_ASSUME(cond)
-//
-// Tell the optimizer that the predicate cond must hold. It is unspecified
-// whether or not cond is actually evaluated.
-//
-#ifdef _MSC_VER
-#define GSL_ASSUME(cond) __assume(cond)
-#elif defined(__GNUC__)
-#define GSL_ASSUME(cond) ((cond) ? static_cast<void>(0) : __builtin_unreachable())
-#else
-#define GSL_ASSUME(cond) static_cast<void>((cond) ? 0 : 0)
-#endif
-
 //
 // GSL.assert: assertions
 //