diff --git a/source/crisscross/cc_attr.h b/source/crisscross/cc_attr.h
index 5ea6028..0a9c69d 100644
--- a/source/crisscross/cc_attr.h
+++ b/source/crisscross/cc_attr.h
@@ -12,23 +12,15 @@
 #ifndef __included_cc_cc_attr_h
 #define __included_cc_cc_attr_h
 
-#if __GNUC__ >= 3
+#if defined(__GNUC__) && __GNUC__ >= 3
 
 #ifndef __pure
 #define __pure         __attribute__ ((pure))
 #endif
 
-/*
-  GCC 3.x doesn't like to inline some of the things that
-  we use __forceinline on.
- */
-#if __GNUC__ > 3
 #ifndef __forceinline
 #define __forceinline  __attribute__ ((always_inline))
 #endif
-#else
-#define __forceinline  inline
-#endif
 
 #ifndef __noreturn
 #define __noreturn     __attribute__ ((noreturn))
@@ -66,21 +58,64 @@
 #define unlikely(x)    __builtin_expect(!!(x), 0)
 #endif
 
-#else
+#define assume(x)    do { if (!(x)) __builtin_unreachable(); } while (0)
+
+#elif defined(_MSC_VER)
+
+#define assume(x)      __assume(x)
 
+#endif
+
+#ifndef __pure
 #define __pure
+#endif
+
+#ifndef __const
 #define __const
+#endif
+
+#ifndef __forceinline
 #define __forceinline  inline
+#endif
+
+#ifndef __noreturn
 #define __noreturn
+#endif
+
+#ifndef __malloc
 #define __malloc
+#endif
+
+#ifndef __must_check
 #define __must_check
+#endif
+
+#ifndef __deprecated
 #define __deprecated
+#endif
+
+#ifndef __used
 #define __used
+#endif
+
+#ifndef __unused_param
 #define __unused_param
+#endif
+
+#ifndef __packed
 #define __packed
+#endif
+
+#ifndef likely
 #define likely(x)      (x)
+#endif
+
+#ifndef unlikely
 #define unlikely(x)    (x)
+#endif
 
+#ifndef assume
+#define assume(x)
 #endif
 
 #endif