diff --git a/include/llvm/Support/Compiler.h b/include/llvm/Support/Compiler.h
index 5ed30a4ef23..b32939eac02 100644
--- a/include/llvm/Support/Compiler.h
+++ b/include/llvm/Support/Compiler.h
@@ -225,8 +225,6 @@
 # define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
 #elif defined(_MSC_VER)
 # define LLVM_BUILTIN_UNREACHABLE __assume(false)
-#else
-# define LLVM_BUILTIN_UNREACHABLE 0
 #endif
 
 /// LLVM_BUILTIN_TRAP - On compilers which support it, expands to an expression
@@ -244,9 +242,11 @@
  || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7))
 // FIXME: Enable on clang when it supports it.
 # define LLVM_ASSUME_ALIGNED(p, a) __builtin_assume_aligned(p, a)
-#else
+#elif defined(LLVM_BUILTIN_UNREACHABLE)
 # define LLVM_ASSUME_ALIGNED(p, a) \
            (((uintptr_t(p) % (a)) == 0) ? (p) : (LLVM_BUILTIN_UNREACHABLE, (p)))
+#else
+# define LLVM_ASSUME_ALIGNED(p, a) (p)
 #endif
 
 #endif