diff --git a/tests/pkg/assets/install/gold/40-exec.gold b/tests/pkg/assets/install/gold/40-exec.gold
new file mode 100644
index 000000000..2fe6c559e
--- /dev/null
+++ b/tests/pkg/assets/install/gold/40-exec.gold
@@ -0,0 +1,5 @@
+exec main.toit
+hello from foo 1.2.3
+hello from bar 2.0.1
+hello from target
+Exit Code: 0
diff --git a/tests/pkg/git-pkg2-gold-test.toit b/tests/pkg/git-pkg2-gold-test.toit
index 3bb77d6fd..d86bbe89c 100644
--- a/tests/pkg/git-pkg2-gold-test.toit
+++ b/tests/pkg/git-pkg2-gold-test.toit
@@ -5,6 +5,8 @@
 import expect show *
 import host.file
 import fs
+import system
+
 import .gold-tester
 
 main args:
@@ -47,3 +49,15 @@ test tester/GoldTester:
 
   readme-path := fs.join tester.working-dir ".packages" "README.md"
   expect (file.is-file readme-path)
+
+  foo-path := tester.package-cache-path "pkg/foo" --version="1.2.3"
+  yaml-path := fs.join foo-path "package.yaml"
+  expect (file.is-file yaml-path)
+  stat := file.stat yaml-path
+  expect-not-null stat
+  mode := stat[file.ST-MODE]
+  if system.platform == system.PLATFORM-WINDOWS:
+    expect (mode & file.WINDOWS-FILE-ATTRIBUTE-READONLY) != 0
+  else:
+    write-bits := 0b010_010_010
+    expect-equals 0 (mode & write-bits)
diff --git a/tests/pkg/gold-tester.toit b/tests/pkg/gold-tester.toit
index b03de6b83..345c5511c 100644
--- a/tests/pkg/gold-tester.toit
+++ b/tests/pkg/gold-tester.toit
@@ -33,7 +33,7 @@ with-tmp-dir [block]:
   try:
     block.call tmp-dir
   finally:
-    directory.rmdir --recursive tmp-dir
+    directory.rmdir --force --recursive tmp-dir
 
 class RunResult_:
   stdout/string
@@ -82,6 +82,14 @@ class GoldTester:
   working-dir -> string:
     return working-dir_
 
+  package-cache-path pkg-suffix/string --version/string -> string:
+    bytes := file.read-contents "$working-dir_/.packages/contents.json"
+    packages := json.decode bytes
+    packages.do: | pkg-name/string pkg-info/Map |
+      if pkg-name.ends-with pkg-suffix:
+        return fs.join working-dir_ ".packages" pkg-info[version]
+    unreachable
+
   normalize str/string -> string:
     str = str.replace --all "localhost:$port_" "localhost:<[*PORT*]>"
     // In lock files, the ':' is replaced with '_'.
diff --git a/tests/pkg/install-gold-test.toit b/tests/pkg/install-gold-test.toit
index 20689b71f..4d37042f8 100644
--- a/tests/pkg/install-gold-test.toit
+++ b/tests/pkg/install-gold-test.toit
@@ -20,24 +20,13 @@ test tester/GoldTester:
     ["exec", "main.toit"],
   ]
 
-  contents := file.read-contents "$tester.working-dir/.packages/contents.json"
-  mapping/Map := json.decode contents
-
-  foo-url/string? := null
-  bar-url/string? := null
-  mapping.do --keys: | key |
-    if key.ends-with "pkg/foo": foo-url = key
-    if key.ends-with "pkg/bar": bar-url = key
-
   foo-version := "1.2.3"
-  foo-rel-path := mapping[foo-url][foo-version]
-  foo-path := "$tester.working-dir/.packages/$foo-rel-path"
+  foo-path := tester.package-cache-path "pkg/foo" --version=foo-version
   expect (file.is-directory foo-path)
   directory.rmdir --recursive --force foo-path
 
   bar-version := "2.0.1"
-  bar-rel-path := mapping[bar-url][bar-version]
-  bar-path := "$tester.working-dir/.packages/$bar-rel-path"
+  bar-path := tester.package-cache-path "pkg/bar" --version=bar-version
   expect (file.is-directory bar-path)
   directory.rmdir --recursive --force bar-path
 
@@ -49,19 +38,15 @@ test tester/GoldTester:
     ["pkg", "install"],
   ]
 
+  tester.gold "40-exec" [
+    ["exec", "main.toit"],
+  ]
+
   // Ensure that the directories are back.
   // We don't guarantee that the directories are the same as before.
-  contents = file.read-contents "$tester.working-dir/.packages/contents.json"
-  mapping = json.decode contents
-
-  mapping.do --keys: | key |
-    if key.ends-with "pkg/foo": foo-url = key
-    if key.ends-with "pkg/bar": bar-url = key
 
-  foo-rel-path = mapping[foo-url][foo-version]
-  foo-path = "$tester.working-dir/.packages/$foo-rel-path"
+  foo-path = tester.package-cache-path "pkg/foo" --version=foo-version
   expect (file.is-directory foo-path)
 
-  bar-rel-path = mapping[bar-url][bar-version]
-  bar-path = "$tester.working-dir/.packages/$bar-rel-path"
+  bar-path = tester.package-cache-path "pkg/bar" --version=bar-version
   expect (file.is-directory bar-path)
diff --git a/tests/pkg/setup.toit b/tests/pkg/setup.toit
index 26b1b32ac..b97445d58 100644
--- a/tests/pkg/setup.toit
+++ b/tests/pkg/setup.toit
@@ -23,4 +23,4 @@ with-test-registry [block]:
 
     block.call tmp-dir
   finally:
-    directory.rmdir --recursive tmp-dir
+    directory.rmdir --force --recursive tmp-dir
diff --git a/tests/pkg/utils_.toit b/tests/pkg/utils_.toit
index 5e8dd8333..5414cdfff 100644
--- a/tests/pkg/utils_.toit
+++ b/tests/pkg/utils_.toit
@@ -3,6 +3,7 @@
 // be found in the tests/LICENSE file.
 
 import host.pipe
+import system
 
 unzip --source/string --target-dir/string -> none:
   // Unzip the given 'source' zip file into the 'target-dir'.
@@ -11,3 +12,16 @@ unzip --source/string --target-dir/string -> none:
     exit-signal := pipe.exit-signal exit-value
     exit-code := pipe.exit-code exit-value
     throw "Failed to unzip '$source' into '$target-dir': $exit-value/$exit-signal"
+
+// A copy of `escape-path` from the utils library of the pkg code.
+escape-path path/string -> string:
+  if system.platform != system.PLATFORM-WINDOWS:
+    return path
+  escaped-path := path.replace --all "#" "##"
+  [ '<', '>', ':', '"', '|', '?', '*', '\\' ].do:
+    escaped-path = escaped-path.replace --all
+        string.from-rune it
+        "#$(%02X it)"
+  if escaped-path.ends-with " " or escaped-path.ends-with ".":
+    escaped-path = "$escaped-path#20"
+  return escaped-path
diff --git a/tools/pkg/project/project.toit b/tools/pkg/project/project.toit
index 6af14e399..745a15103 100644
--- a/tools/pkg/project/project.toit
+++ b/tools/pkg/project/project.toit
@@ -235,6 +235,7 @@ class Project:
         hash = version-hash
       download_ url version --destination=cached-repository-dir --hash=hash
       file.write-contents hash --path=repo-toit-git-path
+      make-read-only_ --recursive cached-repository-dir
     (cached-contents.get url --init=:{:})[version-string] = relative-dir
     write-cached-repository-contents_ cached-contents
     return cached-contents
diff --git a/tools/pkg/utils.toit b/tools/pkg/utils.toit
index a8bf82d04..0d04a6c53 100644
--- a/tools/pkg/utils.toit
+++ b/tools/pkg/utils.toit
@@ -14,6 +14,8 @@
 // directory of this repository.
 
 import encoding.url
+import host.file
+import host.directory
 import fs
 import system
 
@@ -101,3 +103,33 @@ escape-path path/string -> string:
     // a space would normally not be escaped.
     escaped-path = "$escaped-path#20"
   return escaped-path
+
+/**
+Makes the given $path read-only.
+
+If $recursive is true and $path is a directory, makes all files and
+  directories within $path read-only as well.
+*/
+make-read-only_ --recursive/bool path/string -> none:
+  if not recursive or file.is-file path:
+    stat := file.stat path
+    if not stat:
+      return
+    mode := stat[file.ST-MODE]
+    if system.platform == system.PLATFORM-WINDOWS:
+      read-only-bit := file.WINDOWS-FILE-ATTRIBUTE-READONLY
+      if (mode & read-only-bit) != 0: return
+      file.chmod path (mode | read-only-bit)
+      return
+    write-bits := 0b010_010_010
+    if (mode & write-bits) == 0: return
+    file.chmod path (mode & ~write-bits)
+    return
+
+  // If it's not a directory, just ignore it.
+  if not file.is-directory path: return
+
+  stream := directory.DirectoryStream path
+  while child := stream.next:
+    make-read-only_ --recursive (fs.join path child)
+  make-read-only_ --no-recursive path