diff --git a/src/compilersupport_p.h b/src/compilersupport_p.h
index 7f247730..7114e4df 100644
--- a/src/compilersupport_p.h
+++ b/src/compilersupport_p.h
@@ -225,6 +225,8 @@
 #  define unreachable() __builtin_unreachable()
 #elif defined(_MSC_VER)
 #  define unreachable() __assume(0)
+#else
+#  define unreachable()
 #endif
 
 static inline bool add_check_overflow(size_t v1, size_t v2, size_t *r)