diff --git a/.github/workflows/test-on-pr.yml b/.github/workflows/test-on-pr.yml
index 740d741..59d0549 100644
--- a/.github/workflows/test-on-pr.yml
+++ b/.github/workflows/test-on-pr.yml
@@ -82,7 +82,7 @@ jobs:
           # EOL compatibility testing - Node 16 (EOL Sept 2023)
           - node_version: "16"
             npm_version: "8.0.0"
-            yarn_version: "3.6.0"
+            yarn_version: "1.22.0"
             pnpm_version: "8.0.0"
 
     steps:
diff --git a/test/e2e/npm.e2e.spec.js b/test/e2e/npm.e2e.spec.js
index 0e64971..fc23ebb 100644
--- a/test/e2e/npm.e2e.spec.js
+++ b/test/e2e/npm.e2e.spec.js
@@ -60,6 +60,52 @@ describe("E2E: npm coverage", () => {
     );
   });
 
+  it(`safe-chain blocks download of malicious packages already in package.json`, async () => {
+    const shell = await container.openShell("zsh");
+    const npmVersion = (await shell.runCommand("npm --version")).output.trim();
+    const majorVersion = parseInt(npmVersion.split(".")[0]);
+    const minorVersion = parseInt(npmVersion.split(".")[1]);
+    const isBelow10_4 =
+      majorVersion < 10 || (majorVersion === 10 && minorVersion < 4);
+    await shell.runCommand(
+      'echo \'{"name":"test-project","version":"1.0.0","dependencies":{"safe-chain-test":"0.0.1-security"}}\' > package.json'
+    );
+
+    var result = await shell.runCommand("npm install");
+
+    if (isBelow10_4) {
+      assert.ok(
+        result.output.includes("blocked 1 malicious package downloads"),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+      assert.ok(
+        result.output.includes("- safe-chain-test"),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+      assert.ok(
+        result.output.includes(
+          "Exiting without installing malicious packages."
+        ),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+    } else {
+      assert.ok(
+        result.output.includes("Malicious changes detected:"),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+      assert.ok(
+        result.output.includes("- safe-chain-test"),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+      assert.ok(
+        result.output.includes(
+          "Exiting without installing malicious packages."
+        ),
+        `Output did not include expected text. Output was:\n${result.output}`
+      );
+    }
+  });
+
   it("safe-chain blocks npx from executing malicious packages", async () => {
     const shell = await container.openShell("zsh");
     const result = await shell.runCommand("npx safe-chain-test");
diff --git a/test/e2e/pnpm.e2e.spec.js b/test/e2e/pnpm.e2e.spec.js
index db7eb58..c9460e6 100644
--- a/test/e2e/pnpm.e2e.spec.js
+++ b/test/e2e/pnpm.e2e.spec.js
@@ -60,6 +60,28 @@ describe("E2E: pnpm coverage", () => {
     );
   });
 
+  it(`safe-chain blocks download of malicious packages already in package.json`, async () => {
+    const shell = await container.openShell("zsh");
+    await shell.runCommand(
+      'echo \'{"name":"test-project","version":"1.0.0","dependencies":{"safe-chain-test":"0.0.1-security"}}\' > package.json'
+    );
+
+    var result = await shell.runCommand("pnpm install");
+
+    assert.ok(
+      result.output.includes("blocked 1 malicious package downloads"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("- safe-chain-test"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("Exiting without installing malicious packages."),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+  });
+
   it("safe-chain blocks pnpx from executing malicious packages", async () => {
     const shell = await container.openShell("zsh");
     const result = await shell.runCommand("pnpx safe-chain-test");
diff --git a/test/e2e/yarn.e2e.spec.js b/test/e2e/yarn.e2e.spec.js
index fb22b76..df8a88b 100644
--- a/test/e2e/yarn.e2e.spec.js
+++ b/test/e2e/yarn.e2e.spec.js
@@ -60,6 +60,52 @@ describe("E2E: yarn coverage", () => {
     );
   });
 
+  it(`safe-chain blocks download of malicious packages already in package.json`, async () => {
+    const shell = await container.openShell("zsh");
+    await shell.runCommand(
+      'echo \'{"name":"test-project","version":"1.0.0","dependencies":{"safe-chain-test":"0.0.1-security"}}\' > package.json'
+    );
+
+    var result = await shell.runCommand("yarn");
+
+    assert.ok(
+      result.output.includes("blocked 1 malicious package downloads"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("- safe-chain-test"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("Exiting without installing malicious packages."),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+  });
+
+  it(`safe-chain blocks installation of malicious packages`, async () => {
+    const shell = await container.openShell("zsh");
+    const result = await shell.runCommand("yarn add safe-chain-test");
+
+    assert.ok(
+      result.output.includes("Malicious changes detected:"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("- safe-chain-test"),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+    assert.ok(
+      result.output.includes("Exiting without installing malicious packages."),
+      `Output did not include expected text. Output was:\n${result.output}`
+    );
+
+    const listResult = await shell.runCommand("yarn list");
+    assert.ok(
+      !listResult.output.includes("safe-chain-test"),
+      `Malicious package was installed despite safe-chain protection. Output of 'yarn list' was:\n${listResult.output}`
+    );
+  });
+
   it("safe-chain blocks yarn dlx from executing malicious packages", async () => {
     const shell = await container.openShell("zsh");
     const result = await shell.runCommand("yarn dlx safe-chain-test");