diff --git a/webdriver/tests/execute_async_script/execute_async.py b/webdriver/tests/execute_async_script/execute_async.py
index 7c454eaf4ac4f8..03f82ad8ccd5eb 100644
--- a/webdriver/tests/execute_async_script/execute_async.py
+++ b/webdriver/tests/execute_async_script/execute_async.py
@@ -26,6 +26,29 @@ def test_no_browsing_context(session, closed_window):
     assert_error(response, "no such window")
 
 
+@pytest.mark.parametrize("expression,expected", [
+      ("null", None),
+      ("undefined", None),
+      ("true", True),
+      ("false", False),
+      ("23", 23),
+      ("'a string'", "a string"),
+      (
+          # Compute value in the runtime to reduce the potential for
+          # interference from encoding literal bytes or escape sequences in
+          # Python and HTTP.
+          "'a string with a null byte: [' + String.fromCharCode(0) + ']'",
+          "a string with a null byte: [\x00]"
+      )
+    ])
+def test_primitive_serialization(session, expression, expected):
+    response = execute_async_script(
+        session, "arguments[0](%s);" % (expression,)
+    )
+    assert_success(response)
+    assert response.body["value"] == expected
+
+
 @pytest.mark.parametrize("dialog_type", ["alert", "confirm", "prompt"])
 def test_abort_by_user_prompt(session, dialog_type):
     response = execute_async_script(
diff --git a/webdriver/tests/execute_script/execute.py b/webdriver/tests/execute_script/execute.py
index 2af16c1e5e8a3b..d8aa481b25730d 100644
--- a/webdriver/tests/execute_script/execute.py
+++ b/webdriver/tests/execute_script/execute.py
@@ -32,6 +32,27 @@ def test_ending_comment(session):
     assert_success(response, 1)
 
 
+@pytest.mark.parametrize("expression,expected", [
+      ("null", None),
+      ("undefined", None),
+      ("true", True),
+      ("false", False),
+      ("23", 23),
+      ("'a string'", "a string"),
+      (
+          # Compute value in the runtime to reduce the potential for
+          # interference from encoding literal bytes or escape sequences in
+          # Python and HTTP.
+          "'a string with a null byte: [' + String.fromCharCode(0) + ']'",
+          "a string with a null byte: [\x00]"
+      )
+    ])
+def test_primitive_serialization(session, expression, expected):
+    response = execute_script(session, "return %s;" % (expression,))
+    assert_success(response)
+    assert response.body["value"] == expected
+
+
 @pytest.mark.parametrize("dialog_type", ["alert", "confirm", "prompt"])
 def test_abort_by_user_prompt(session, dialog_type):
     response = execute_script(