diff --git a/platforms/posix/src/px4/windows/tests/CMakeLists.txt b/platforms/posix/src/px4/windows/tests/CMakeLists.txt
index 4a1a0b41f7..fd0033eeed 100644
--- a/platforms/posix/src/px4/windows/tests/CMakeLists.txt
+++ b/platforms/posix/src/px4/windows/tests/CMakeLists.txt
@@ -43,11 +43,24 @@ if(NOT BUILD_TESTING)
 	return()
 endif()
 
+# Shared static-init hook that silences the MSVC Debug CRT invalid
+# parameter handler so tests that exercise bad-fd / bad-handle paths do
+# not abort with a debug-time assertion dialog. Linked into every
+# Windows shim test target as an EXTRA_SRC.
+set(_px4_windows_shim_silencer
+	${CMAKE_CURRENT_SOURCE_DIR}/test_main_silence.cpp
+)
+
 # Headers-only tests (libgen, dirent, sched, syslog, mman, time, unistd,
 # getopt, fcntl). The translation unit pulls the shim headers via the
-# existing windows_shim include path; no extra link libraries are
-# required beyond gtest itself.
-px4_add_unit_gtest(SRC test_windows_shim_headers.cpp)
+# existing windows_shim include path; the inline fcntl() routes
+# O_NONBLOCK changes through ioctlsocket() so we need ws2_32 to satisfy
+# the symbol even on the headers-only target.
+px4_add_unit_gtest(
+	SRC test_windows_shim_headers.cpp
+	EXTRA_SRCS ${_px4_windows_shim_silencer}
+	LINKLIBS ws2_32
+)
 
 # Source-defined shim tests (errno_map, env, sysconf, mman, flock, dlfcn,
 # ids, if_query, resolver, socket loopback). Pulls in the standalone
@@ -69,7 +82,7 @@ set(_px4_windows_shim_test_srcs
 
 px4_add_unit_gtest(
 	SRC test_windows_shim_runtime.cpp
-	EXTRA_SRCS ${_px4_windows_shim_test_srcs}
+	EXTRA_SRCS ${_px4_windows_shim_test_srcs} ${_px4_windows_shim_silencer}
 	INCLUDES
 		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
 		${_px4_windows_shim_root}/include
@@ -79,6 +92,7 @@ px4_add_unit_gtest(
 # poll() inline implementation - header-only test.
 px4_add_unit_gtest(
 	SRC test_windows_shim_poll.cpp
+	EXTRA_SRCS ${_px4_windows_shim_silencer}
 	INCLUDES
 		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
 	LINKLIBS ws2_32
@@ -88,6 +102,7 @@ px4_add_unit_gtest(
 # POSIX names route to MSVC CRT primitives via inline shim wrappers.
 px4_add_unit_gtest(
 	SRC test_windows_shim_io.cpp
+	EXTRA_SRCS ${_px4_windows_shim_silencer}
 	INCLUDES
 		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
 )
diff --git a/platforms/posix/src/px4/windows/tests/test_main_silence.cpp b/platforms/posix/src/px4/windows/tests/test_main_silence.cpp
new file mode 100644
index 0000000000..3d134e299f
--- /dev/null
+++ b/platforms/posix/src/px4/windows/tests/test_main_silence.cpp
@@ -0,0 +1,67 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2026 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file test_main_silence.cpp
+ *
+ * Suppress the MSVC Debug CRT invalid-parameter handler so unit tests that
+ * intentionally exercise bad-fd / bad-handle paths (e.g. fcntl(0, 0xBAD),
+ * flock(-1, ...), _open on a closed fd) do not abort with a debug-time
+ * assertion dialog. Without this hook the Debug CRT raises Watson and
+ * terminates the process before gtest can record the EXPECT_* result.
+ *
+ * Linked into every shim unit test target via
+ * platforms/posix/src/px4/windows/tests/CMakeLists.txt; takes effect at
+ * static-init time before main() runs gtest.
+ */
+
+#ifdef _WIN32
+#include <stdlib.h>
+#include <crtdbg.h>
+
+namespace
+{
+static void silent_invalid_param(const wchar_t *, const wchar_t *, const wchar_t *,
+				 unsigned, uintptr_t) {}
+struct InstallSilencer {
+	InstallSilencer()
+	{
+		_set_invalid_parameter_handler(silent_invalid_param);
+		_CrtSetReportMode(_CRT_ASSERT, 0);
+		_CrtSetReportMode(_CRT_ERROR, 0);
+		_CrtSetReportMode(_CRT_WARN, 0);
+	}
+};
+static InstallSilencer kInstallSilencer;
+} // namespace
+#endif