diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 358a2b8f..be713bca 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -13,7 +13,9 @@ function (expect_compile_error code)
   if (compiles)
     error("No compile error for: ${code}")
   endif ()
+  unset(compiles CACHE)
 endfunction ()
 
 # Writing a wide character to a character stream Writer is forbidden.
 expect_compile_error("fmt::Writer() << L'a';")
+expect_compile_error("fmt::Writer() << fmt::pad(\"abc\", 5, L' ');")