diff --git a/.github/workflows/scalatest.yml b/.github/workflows/scalatest.yml
index 016092c8bd..2bd419385d 100644
--- a/.github/workflows/scalatest.yml
+++ b/.github/workflows/scalatest.yml
@@ -24,8 +24,6 @@ jobs:
         uses: actions/cache@v3
         with:
           path: |
-            ~/.cache/coursier
-            ~/.mill/ammonite
             out
             !**/assembly.dest
             !**/assembly.json
diff --git a/build.sc b/build.sc
index 51bfda94d4..bbb3fe595a 100644
--- a/build.sc
+++ b/build.sc
@@ -370,6 +370,7 @@ object util {
       os.proc("git", "config", "advice.detachedHead", "false").call(cwd = T.dest)
       os.proc("git", "checkout", "FETCH_HEAD").call(cwd = T.dest)
       os.walk(T.dest).foreach(_.toIO.setWritable(true))
+      os.remove.all(T.dest / ".git")
       T.dest
     }
   }
@@ -403,11 +404,21 @@ object viper extends ScalaModule {
   object silverGit extends GitModule {
     def url = T { "https://github.com/viperproject/silver.git" }
     def commitish = T { "ae4a12399cd0b42bedabf01be2cda93700244bd6" }
+    def filteredRepo = T {
+      val workspace = repo()
+      os.remove.all(workspace / "src" / "test")
+      workspace
+    }
   }
 
   object siliconGit extends GitModule {
     def url = T { "https://github.com/viperproject/silicon.git" }
     def commitish = T { "a60324dd46923b861bae7b4a40f807227d693fc3" }
+    def filteredRepo = T {
+      val workspace = repo()
+      os.remove.all(workspace / "src" / "test")
+      workspace
+    }
   }
 
   object carbonGit extends GitModule {
@@ -419,7 +430,7 @@ object viper extends ScalaModule {
     override def scalaVersion = "2.13.10"
     override def scalacOptions = T { Seq("-Xno-patmat-analysis", "-nowarn") }
     def repo = silverGit
-    override def sources = T.sources { repo.repo() / "src" / "main" / "scala" }
+    override def sources = T.sources { repo.filteredRepo() / "src" / "main" / "scala" }
     override def ivyDeps = settings.deps.log ++ Agg(
       ivy"org.scala-lang:scala-reflect:2.13.10",
       ivy"org.scalatest::scalatest:3.1.2",
@@ -450,20 +461,20 @@ object viper extends ScalaModule {
     object common extends ScalaModule {
       override def scalaVersion = "2.13.10"
       override def scalacOptions = T { Seq("-Xno-patmat-analysis", "-nowarn") }
-      override def sources = T.sources { silicon.repo.repo() / "common" / "src" / "main" / "scala" }
+      override def sources = T.sources { silicon.repo.filteredRepo() / "common" / "src" / "main" / "scala" }
       override def moduleDeps = Seq(silver)
     }
 
     override def scalaVersion = "2.13.10"
     override def scalacOptions = T { Seq("-Xno-patmat-analysis", "-nowarn") }
     def repo = siliconGit
-    override def sources = T.sources { repo.repo() / "src" / "main" / "scala" }
+    override def sources = T.sources { repo.filteredRepo() / "src" / "main" / "scala" }
     override def ivyDeps = settings.deps.log ++ Agg(
       ivy"org.apache.commons:commons-pool2:2.9.0",
       ivy"io.spray::spray-json:1.3.6",
     )
     override def resources = T.sources {
-      repo.repo() / "src" / "main" / "resources"
+      repo.filteredRepo() / "src" / "main" / "resources"
     }
     override def unmanagedClasspath = Agg(external.z3.classPath())
     override def moduleDeps = Seq(silver, common, buildInfo)