diff --git a/src/boost_process_compat.h b/src/compat/boost_process.h
similarity index 92%
rename from src/boost_process_compat.h
rename to src/compat/boost_process.h
index d5441db3a12..47907e97695 100644
--- a/src/boost_process_compat.h
+++ b/src/compat/boost_process.h
@@ -1,5 +1,5 @@
 /**
- * @file src/boost_process_compat.h
+ * @file src/compat/boost_process.h
  * @brief Includes Boost.Process while isolating third-party deprecation diagnostics.
  */
 #pragma once
diff --git a/src/compat/moonlight.h b/src/compat/moonlight.h
new file mode 100644
index 00000000000..e2896aa6cdc
--- /dev/null
+++ b/src/compat/moonlight.h
@@ -0,0 +1,36 @@
+/**
+ * @file src/compat/moonlight.h
+ * @brief Import Moonlight's C declarations without changing C++ errno definitions.
+ */
+#pragma once
+
+// standard includes
+// Load the CRT definitions before saving them, even when this is the first include.
+#include <cerrno>
+
+// PlatformSockets.h maps these names to Winsock values for Moonlight's C code.
+// Let that code see its mappings, but do not leak them into Boost or the C++ library.
+#ifdef _WIN32
+  #pragma push_macro("EAGAIN")
+  #pragma push_macro("EINTR")
+  #pragma push_macro("EWOULDBLOCK")
+  #pragma push_macro("EINPROGRESS")
+  #pragma push_macro("ETIMEDOUT")
+  #pragma push_macro("ECONNREFUSED")
+  #pragma push_macro("EMSGSIZE")
+#endif
+
+// lib includes
+extern "C" {
+#include <moonlight-common-c/src/Limelight-internal.h>
+}
+
+#ifdef _WIN32
+  #pragma pop_macro("EMSGSIZE")
+  #pragma pop_macro("ECONNREFUSED")
+  #pragma pop_macro("ETIMEDOUT")
+  #pragma pop_macro("EINPROGRESS")
+  #pragma pop_macro("EWOULDBLOCK")
+  #pragma pop_macro("EINTR")
+  #pragma pop_macro("EAGAIN")
+#endif
diff --git a/src/platform/common.h b/src/platform/common.h
index 62961d7a310..7919f49d105 100644
--- a/src/platform/common.h
+++ b/src/platform/common.h
@@ -20,7 +20,7 @@
 
 // local includes
 #ifndef _WIN32
-  #include "src/boost_process_compat.h"
+  #include "src/compat/boost_process.h"
 #endif
 #include "src/config.h"
 #include "src/logging.h"
diff --git a/src/platform/linux/misc.cpp b/src/platform/linux/misc.cpp
index b89b9b97dd0..143075b534c 100644
--- a/src/platform/linux/misc.cpp
+++ b/src/platform/linux/misc.cpp
@@ -59,7 +59,7 @@
 // local includes
 #include "graphics.h"
 #include "misc.h"
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 #include "src/config.h"
 #include "src/entry_handler.h"
 #include "src/globals.h"
diff --git a/src/platform/macos/misc.mm b/src/platform/macos/misc.mm
index 9fde3784788..e4ed3c27872 100644
--- a/src/platform/macos/misc.mm
+++ b/src/platform/macos/misc.mm
@@ -38,7 +38,7 @@
 
 // local includes
 #include "misc.h"
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 #include "src/config.h"
 #include "src/entry_handler.h"
 #include "src/logging.h"
diff --git a/src/platform/windows/display_base.cpp b/src/platform/windows/display_base.cpp
index 2a013367107..f97b6933d7a 100644
--- a/src/platform/windows/display_base.cpp
+++ b/src/platform/windows/display_base.cpp
@@ -13,7 +13,7 @@
 
 // local includes required before library includes
 // Boost.Process must be included before MinHook pulls in Windows.h so Boost.Asio sees WinSock2.h first.
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 
 // lib includes
 #include <boost/algorithm/string/join.hpp>
diff --git a/src/platform/windows/misc.cpp b/src/platform/windows/misc.cpp
index 9556275828d..d68b928d0ed 100644
--- a/src/platform/windows/misc.cpp
+++ b/src/platform/windows/misc.cpp
@@ -30,7 +30,7 @@
 #include <boost/range/algorithm/find_if.hpp>
 
 // local includes required before platform includes
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 
 // platform includes
 // prevent clang format from "optimizing" the header include order
diff --git a/src/process.h b/src/process.h
index 132178be709..774b0bacd26 100644
--- a/src/process.h
+++ b/src/process.h
@@ -20,7 +20,7 @@
 #include "config.h"
 #include "platform/common.h"
 #include "rtsp.h"
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 #include "utility.h"
 
 /**
diff --git a/src/rtsp.cpp b/src/rtsp.cpp
index 71253733ce7..7f8c97d792d 100644
--- a/src/rtsp.cpp
+++ b/src/rtsp.cpp
@@ -4,8 +4,9 @@
  */
 #define BOOST_BIND_GLOBAL_PLACEHOLDERS
 
+#include "compat/moonlight.h"
+
 extern "C" {
-#include <moonlight-common-c/src/Limelight-internal.h>
 #include <moonlight-common-c/src/Rtsp.h>
 }
 
diff --git a/src/stream.cpp b/src/stream.cpp
index 2f2db0c2fc9..be458d50161 100644
--- a/src/stream.cpp
+++ b/src/stream.cpp
@@ -17,11 +17,8 @@
 #include <openssl/err.h>
 #include <rs.h>
 
-extern "C" {
-  // clang-format off
-#include <moonlight-common-c/src/Limelight-internal.h>
-  // clang-format on
-}
+// Keep this separate so clang-format preserves the include order.
+#include "compat/moonlight.h"
 
 // local includes
 #include "config.h"
diff --git a/tests/integration/test_external_commands.cpp b/tests/integration/test_external_commands.cpp
index adf730a9041..997ae166c08 100644
--- a/tests/integration/test_external_commands.cpp
+++ b/tests/integration/test_external_commands.cpp
@@ -13,7 +13,7 @@
 #include <vector>
 
 // local includes
-#include "src/boost_process_compat.h"
+#include "src/compat/boost_process.h"
 #include "src/platform/common.h"
 
 // Test data structure for parameterized testing
diff --git a/tests/unit/moonlight_common_first_include.cpp b/tests/unit/moonlight_common_first_include.cpp
new file mode 100644
index 00000000000..e12018bc13c
--- /dev/null
+++ b/tests/unit/moonlight_common_first_include.cpp
@@ -0,0 +1,69 @@
+/**
+ * @file tests/unit/moonlight_common_first_include.cpp
+ * @brief Capture errno when the Moonlight wrapper is the first include in its translation unit.
+ */
+
+// local includes
+#include <src/compat/moonlight.h>
+
+namespace {
+  // Capture before any other include. Missing macros use zero only to keep a
+  // broken wrapper testable at runtime; the separate completeness flag must pass.
+  constexpr int errno_after_first_include[7] /* NOSONAR(cpp:S5945): No extra headers before the errno snapshot. */ {
+#ifdef EAGAIN
+    EAGAIN,
+#else
+    0,
+#endif
+#ifdef EINTR
+    EINTR,
+#else
+    0,
+#endif
+#ifdef EWOULDBLOCK
+    EWOULDBLOCK,
+#else
+    0,
+#endif
+#ifdef EINPROGRESS
+    EINPROGRESS,
+#else
+    0,
+#endif
+#ifdef ETIMEDOUT
+    ETIMEDOUT,
+#else
+    0,
+#endif
+#ifdef ECONNREFUSED
+    ECONNREFUSED,
+#else
+    0,
+#endif
+#ifdef EMSGSIZE
+    EMSGSIZE
+#else
+    0
+#endif
+  };  ///< Errno values captured immediately after the first include.
+
+#if defined(EAGAIN) && defined(EINTR) && defined(EWOULDBLOCK) && defined(EINPROGRESS) && defined(ETIMEDOUT) && defined(ECONNREFUSED) && defined(EMSGSIZE)
+  constexpr bool errno_complete = true;  ///< Every required errno name was defined.
+#else
+  constexpr bool errno_complete = false;  ///< At least one required errno name was absent.
+#endif
+}  // namespace
+
+namespace moonlight_common_tests {
+  /**
+   * @brief Copy the first-include errno snapshot without sharing library types across translation units.
+   * @param values Destination for seven errno values.
+   * @return Whether all seven errno names were defined.
+   */
+  bool first_include_errno(int *values) {
+    for (int index = 0; index < 7; ++index) {
+      values[index] = errno_after_first_include[index];
+    }
+    return errno_complete;
+  }
+}  // namespace moonlight_common_tests
diff --git a/tests/unit/test_moonlight_common.cpp b/tests/unit/test_moonlight_common.cpp
new file mode 100644
index 00000000000..de69c82e311
--- /dev/null
+++ b/tests/unit/test_moonlight_common.cpp
@@ -0,0 +1,111 @@
+/**
+ * @file tests/unit/test_moonlight_common.cpp
+ * @brief Verify that importing Moonlight does not change C++ errno constants.
+ */
+
+// The shared test header includes Boost. Keep it after the errno snapshots and
+// the explicit Boost include so it cannot mask this regression.
+
+// standard includes
+#include <array>
+#include <cerrno>
+
+namespace {
+  constexpr std::array<int, 7> errno_before_moonlight {
+    EAGAIN,
+    EINTR,
+    EWOULDBLOCK,
+    EINPROGRESS,
+    ETIMEDOUT,
+    ECONNREFUSED,
+    EMSGSIZE
+  };  ///< CRT errno values before including Moonlight.
+}
+
+// local includes
+// Capture errno immediately after including Moonlight.
+#include <src/compat/moonlight.h>  // NOSONAR(cpp:S954): The baseline must precede this include.
+
+namespace {
+  constexpr std::array<int, 7> errno_after_moonlight {
+    EAGAIN,
+    EINTR,
+    EWOULDBLOCK,
+    EINPROGRESS,
+    ETIMEDOUT,
+    ECONNREFUSED,
+    EMSGSIZE
+  };  ///< Errno values immediately after including Moonlight.
+}
+
+// lib includes
+// Boost must be parsed after the wrapper for this regression test.
+#include <boost/system/error_code.hpp>
+
+// test includes
+#include "../tests_common.h"
+
+namespace moonlight_common_tests {
+  /**
+   * @brief Copy the first-include errno snapshot without sharing library types across translation units.
+   * @param values Destination for seven errno values in the baseline array's order.
+   * @return Whether all seven errno names were defined.
+   */
+  bool first_include_errno(int *values);
+}  // namespace moonlight_common_tests
+
+/**
+ * @brief Including Moonlight preserves the CRT errno values.
+ */
+TEST(MoonlightCommonTests, PreservesCrtErrno) {
+  EXPECT_EQ(errno_before_moonlight, errno_after_moonlight);
+}
+
+/**
+ * @brief Boost's error constants match the original CRT errno values.
+ */
+TEST(MoonlightCommonTests, PreservesBoostErrno) {
+  const std::array<int, 7> boost_errno {
+    boost::system::errc::resource_unavailable_try_again,
+    boost::system::errc::interrupted,
+    boost::system::errc::operation_would_block,
+    boost::system::errc::operation_in_progress,
+    boost::system::errc::timed_out,
+    boost::system::errc::connection_refused,
+    boost::system::errc::message_size
+  };
+  EXPECT_EQ(errno_before_moonlight, boost_errno);
+}
+
+/**
+ * @brief The wrapper initializes errno even when it is the first include.
+ */
+TEST(MoonlightCommonTests, FirstIncludePreservesCrtErrno) {
+  std::array<int, 7> first_include_values {};
+  EXPECT_TRUE(moonlight_common_tests::first_include_errno(first_include_values.data()));
+  EXPECT_EQ(errno_before_moonlight, first_include_values);
+}
+
+/**
+ * @brief Native connection-refused errors match Boost's generic condition.
+ */
+TEST(MoonlightCommonTests, ConnectionRefusedCondition) {
+#ifdef _WIN32
+  const boost::system::error_code ec {WSAECONNREFUSED, boost::system::system_category()};
+#else
+  const boost::system::error_code ec {ECONNREFUSED, boost::system::system_category()};
+#endif
+  EXPECT_EQ(ec, boost::system::errc::connection_refused);
+}
+
+/**
+ * @brief Native timeouts match Boost's generic condition.
+ */
+TEST(MoonlightCommonTests, TimedOutCondition) {
+#ifdef _WIN32
+  const boost::system::error_code ec {WSAETIMEDOUT, boost::system::system_category()};
+#else
+  const boost::system::error_code ec {ETIMEDOUT, boost::system::system_category()};
+#endif
+  EXPECT_EQ(ec, boost::system::errc::timed_out);
+}