diff --git a/src/compat/assumptions.h b/src/compat/assumptions.h
--- a/src/compat/assumptions.h
+++ b/src/compat/assumptions.h
@@ -54,7 +54,8 @@
 // http://eel.is/c++draft/basic.memobj#def:byte
 // http://eel.is/c++draft/expr.sizeof#1
 // http://eel.is/c++draft/cstdint#syn
-static_assert(std::is_same<uint8_t, unsigned char>::value);
+static_assert(std::is_same<uint8_t, unsigned char>::value,
+              "uint8_t is an alias of unsigned char");
 
 // Some important things we are NOT assuming (non-exhaustive list):
 // * We are NOT assuming a specific value for sizeof(std::size_t).