diff --git a/clang-tools-extra/test/clang-tidy/cppcoreguidelines-owning-memory-legacy-functions.cpp b/clang-tools-extra/test/clang-tidy/cppcoreguidelines-owning-memory-legacy-functions.cpp
index cbdb317be968..5785e9f7d0cd 100644
--- a/clang-tools-extra/test/clang-tidy/cppcoreguidelines-owning-memory-legacy-functions.cpp
+++ b/clang-tools-extra/test/clang-tidy/cppcoreguidelines-owning-memory-legacy-functions.cpp
@@ -10,7 +10,7 @@ using owner = T;
 } // namespace gsl
 
 extern "C" {
-using size_t = unsigned long long;
+using size_t = decltype(sizeof(void*));
 using FILE = int;
 
 void *malloc(size_t ByteCount);