diff --git a/test/static/si_test.cpp b/test/static/si_test.cpp
index 8ce65935..0599469b 100644
--- a/test/static/si_test.cpp
+++ b/test/static/si_test.cpp
@@ -61,8 +61,9 @@ static_assert(1 * Rm == 1'000'000'000'000'000'000 * Gm);
 static_assert(1 * Qm == 1'000'000'000'000'000'000 * Tm);
 
 // check for invalid prefixes
-template<template<auto U> typename prefix, auto V1>
-concept can_not_be_prefixed = Unit<std::remove_const_t<decltype(V1)>> && !requires { typename prefix<V1>; };
+template<template<typename U> typename prefix, auto V1>
+concept can_not_be_prefixed =
+  Unit<std::remove_const_t<decltype(V1)>> && !requires { typename prefix<std::remove_const_t<decltype(V1)>>; };
 
 static_assert(can_not_be_prefixed<si::milli_, si::degree_Celsius>);
 static_assert(can_not_be_prefixed<si::milli_, si::minute>);