diff --git a/build_system/prepare.rs b/build_system/prepare.rs
index bc249f4cdab3..115575bff51b 100644
--- a/build_system/prepare.rs
+++ b/build_system/prepare.rs
@@ -18,10 +18,6 @@ pub(crate) fn prepare(dirs: &Dirs, rustc: &Path) {
 
     // FIXME do this on the fly?
     prepare_stdlib(dirs, rustc);
-
-    super::tests::RAND_REPO.patch(dirs);
-    super::tests::REGEX_REPO.patch(dirs);
-    super::tests::PORTABLE_SIMD_REPO.patch(dirs);
 }
 
 fn prepare_stdlib(dirs: &Dirs, rustc: &Path) {
diff --git a/build_system/tests.rs b/build_system/tests.rs
index 5502e2a23c6c..d104efd61e59 100644
--- a/build_system/tests.rs
+++ b/build_system/tests.rs
@@ -133,6 +133,8 @@ static LIBCORE_TESTS: CargoProject = CargoProject::new(&LIBCORE_TESTS_SRC, "core
 
 const EXTENDED_SYSROOT_SUITE: &[TestCase] = &[
     TestCase::custom("test.rust-random/rand", &|runner| {
+        RAND_REPO.patch(&runner.dirs);
+
         RAND.clean(&runner.dirs);
 
         if runner.is_native {
@@ -168,6 +170,8 @@ const EXTENDED_SYSROOT_SUITE: &[TestCase] = &[
         }
     }),
     TestCase::custom("test.regex-shootout-regex-dna", &|runner| {
+        REGEX_REPO.patch(&runner.dirs);
+
         REGEX.clean(&runner.dirs);
 
         let mut build_cmd = REGEX.build(&runner.target_compiler, &runner.dirs);
@@ -200,6 +204,8 @@ const EXTENDED_SYSROOT_SUITE: &[TestCase] = &[
         }
     }),
     TestCase::custom("test.regex", &|runner| {
+        REGEX_REPO.patch(&runner.dirs);
+
         REGEX.clean(&runner.dirs);
 
         if runner.is_native {
@@ -216,6 +222,8 @@ const EXTENDED_SYSROOT_SUITE: &[TestCase] = &[
         }
     }),
     TestCase::custom("test.portable-simd", &|runner| {
+        PORTABLE_SIMD_REPO.patch(&runner.dirs);
+
         PORTABLE_SIMD.clean(&runner.dirs);
 
         let mut build_cmd = PORTABLE_SIMD.build(&runner.target_compiler, &runner.dirs);