diff --git a/crates/vm/src/stdlib/_winapi.rs b/crates/vm/src/stdlib/_winapi.rs
index 6f495299a..5462ba7ca 100644
--- a/crates/vm/src/stdlib/_winapi.rs
+++ b/crates/vm/src/stdlib/_winapi.rs
@@ -246,20 +246,25 @@ mod _winapi {
         args: CreateProcessArgs,
         vm: &VirtualMachine,
     ) -> PyResult<(WinHandle, WinHandle, u32, u32)> {
+        // Default failed startup attribute lookups as CPython does. Keep value
+        // conversion errors separate from lookup failures.
         macro_rules! si_attr {
             ($attr:ident, $t:ty) => {{
-                <Option<$t>>::try_from_object(
-                    vm,
-                    args.startup_info.get_attr(stringify!($attr), vm)?,
-                )?
-                .unwrap_or(0) as _
+                args.startup_info
+                    .get_attr(stringify!($attr), vm)
+                    .ok()
+                    .map(|obj| <Option<$t>>::try_from_object(vm, obj))
+                    .transpose()?
+                    .flatten()
+                    .unwrap_or(0) as _
             }};
             ($attr:ident) => {{
-                <Option<_>>::try_from_object(
-                    vm,
-                    args.startup_info.get_attr(stringify!($attr), vm)?,
-                )?
-                .unwrap_or(0)
+                args.startup_info
+                    .get_attr(stringify!($attr), vm)
+                    .ok()
+                    .map(|obj| TryFromObject::try_from_object(vm, obj))
+                    .transpose()?
+                    .unwrap_or(0)
             }};
         }
         let startup_info = host_winapi::StartupInfoData {
@@ -275,7 +280,13 @@ mod _winapi {
             .map(|m| getenvironment(m, vm))
             .transpose()?;
 
-        let handle_list = get_handle_list(args.startup_info.get_attr("lpAttributeList", vm)?, vm)?;
+        let handle_list = args
+            .startup_info
+            .get_attr("lpAttributeList", vm)
+            .ok()
+            .map(|obj| get_handle_list(obj, vm))
+            .transpose()?
+            .flatten();
 
         // Validate no embedded null bytes in command name and command line
         // before handing the strings off; to_wide_cstring rejects interior NULs.
diff --git a/extra_tests/snippets/stdlib_winapi.py b/extra_tests/snippets/stdlib_winapi.py
index ef1cad44c..31aca0762 100644
--- a/extra_tests/snippets/stdlib_winapi.py
+++ b/extra_tests/snippets/stdlib_winapi.py
@@ -4,36 +4,86 @@ import sys
 
 from testutils import assert_raises
 
-if sys.platform == "win32":
-    import _winapi
+if sys.platform != "win32":
+    sys.exit(0)
 
-    # Every call fails before a host operation. ReportEvent overflow cases
-    # also retain an embedded NUL as an independent safety barrier.
-    assert _winapi.EVENTLOG_SUCCESS == 0
-    assert _winapi.EVENTLOG_ERROR_TYPE == 1
-    assert _winapi.EVENTLOG_WARNING_TYPE == 2
-    assert _winapi.EVENTLOG_INFORMATION_TYPE == 4
-    assert _winapi.EVENTLOG_AUDIT_SUCCESS == 8
-    assert _winapi.EVENTLOG_AUDIT_FAILURE == 16
+import _winapi
 
-    assert_raises(TypeError, _winapi.RegisterEventSource, 1, "source\0")
-    assert_raises(TypeError, _winapi.RegisterEventSource, None, 1)
-    assert_raises(TypeError, _winapi.RegisterEventSource, None, None)
-    assert_raises(ValueError, _winapi.RegisterEventSource, None, "source\0")
-    assert_raises(ValueError, _winapi.RegisterEventSource, "server\0", "source\0")
-    assert_raises(ValueError, _winapi.RegisterEventSource, "", "source\0")
-    assert_raises(TypeError, _winapi.DeregisterEventSource, "invalid handle")
-    assert_raises(TypeError, _winapi.DeregisterEventSource, None)
-    assert_raises(
-        TypeError, _winapi.ReportEvent, "invalid handle", 0, 0, 0, "message\0"
-    )
-    assert_raises(ValueError, _winapi.ReportEvent, 0, 0, 0, 0, "message\0")
-    assert_raises(TypeError, _winapi.ReportEvent, 0, 0, 0, 0, None)
-    for index, bits in ((1, 16), (2, 16), (3, 32)):
-        for invalid, exception in ((-1, ValueError), (1 << bits, OverflowError)):
-            arguments = [0, 0, 0, 0, "message\0"]
-            arguments[index] = invalid
-            assert_raises(exception, _winapi.ReportEvent, *arguments)
+# Every call fails before a host operation. ReportEvent overflow cases
+# also retain an embedded NUL as an independent safety barrier.
+assert _winapi.EVENTLOG_SUCCESS == 0
+assert _winapi.EVENTLOG_ERROR_TYPE == 1
+assert _winapi.EVENTLOG_WARNING_TYPE == 2
+assert _winapi.EVENTLOG_INFORMATION_TYPE == 4
+assert _winapi.EVENTLOG_AUDIT_SUCCESS == 8
+assert _winapi.EVENTLOG_AUDIT_FAILURE == 16
+
+assert_raises(TypeError, _winapi.RegisterEventSource, 1, "source\0")
+assert_raises(TypeError, _winapi.RegisterEventSource, None, 1)
+assert_raises(TypeError, _winapi.RegisterEventSource, None, None)
+assert_raises(ValueError, _winapi.RegisterEventSource, None, "source\0")
+assert_raises(ValueError, _winapi.RegisterEventSource, "server\0", "source\0")
+assert_raises(ValueError, _winapi.RegisterEventSource, "", "source\0")
+assert_raises(TypeError, _winapi.DeregisterEventSource, "invalid handle")
+assert_raises(TypeError, _winapi.DeregisterEventSource, None)
+assert_raises(TypeError, _winapi.ReportEvent, "invalid handle", 0, 0, 0, "message\0")
+assert_raises(ValueError, _winapi.ReportEvent, 0, 0, 0, 0, "message\0")
+assert_raises(TypeError, _winapi.ReportEvent, 0, 0, 0, 0, None)
+for index, bits in ((1, 16), (2, 16), (3, 32)):
+    for invalid, exception in ((-1, ValueError), (1 << bits, OverflowError)):
         arguments = [0, 0, 0, 0, "message\0"]
-        arguments[index] = "invalid integer"
-        assert_raises(TypeError, _winapi.ReportEvent, *arguments)
+        arguments[index] = invalid
+        assert_raises(exception, _winapi.ReportEvent, *arguments)
+    arguments = [0, 0, 0, 0, "message\0"]
+    arguments[index] = "invalid integer"
+    assert_raises(TypeError, _winapi.ReportEvent, *arguments)
+
+
+import subprocess
+
+
+class PartialStartupInfo:
+    dwFlags = 0
+
+    def __getattr__(self, name):
+        raise ValueError(name)
+
+
+for startup in (None, PartialStartupInfo()):
+    process, thread, _, _ = _winapi.CreateProcess(
+        sys.executable,
+        subprocess.list2cmdline([sys.executable, "-c", "pass"]),
+        None,
+        None,
+        False,
+        _winapi.CREATE_NO_WINDOW,
+        None,
+        None,
+        startup,
+    )
+    try:
+        status = _winapi.WaitForSingleObject(process, 10000)
+        if status != _winapi.WAIT_OBJECT_0:
+            _winapi.TerminateProcess(process, 1)
+            _winapi.WaitForSingleObject(process, 10000)
+        assert status == _winapi.WAIT_OBJECT_0
+        assert _winapi.GetExitCodeProcess(process) == 0
+    finally:
+        _winapi.CloseHandle(thread)
+        _winapi.CloseHandle(process)
+
+startup = subprocess.STARTUPINFO()
+startup.dwFlags = "invalid"
+assert_raises(
+    TypeError,
+    _winapi.CreateProcess,
+    None,
+    "invalid\0",
+    None,
+    None,
+    False,
+    0,
+    None,
+    None,
+    startup,
+)