diff --git a/src/testlib/qtestcrashhandler_p.h b/src/testlib/qtestcrashhandler_p.h
index d11ea964b58..16209eaae36 100644
--- a/src/testlib/qtestcrashhandler_p.h
+++ b/src/testlib/qtestcrashhandler_p.h
@@ -28,49 +28,9 @@
 #include <unistd.h>
 #endif
 
-#ifdef Q_OS_WIN
-#include <iostream>
-#endif
-
 QT_BEGIN_NAMESPACE
 namespace QTest {
 namespace CrashHandler {
-#if defined(Q_OS_UNIX) && (!defined(Q_OS_WASM) || QT_CONFIG(thread))
-    struct iovec IoVec(struct iovec vec);
-    struct iovec IoVec(const char *str);
-
-    template <typename... Args> static ssize_t writeToStderr(Args &&... args)
-    {
-        struct iovec vec[] = { IoVec(std::forward<Args>(args))... };
-        return ::writev(STDERR_FILENO, vec, std::size(vec));
-    }
-
-    // async-signal-safe conversion from int to string
-    struct AsyncSafeIntBuffer
-    {
-        // digits10 + 1 for all possible digits
-        // +1 for the sign
-        // +1 for the terminating null
-        static constexpr int Digits10 = std::numeric_limits<int>::digits10 + 3;
-        std::array<char, Digits10> array;
-        constexpr AsyncSafeIntBuffer() : array{} {}     // initializes array
-        AsyncSafeIntBuffer(Qt::Initialization) {}       // leaves array uninitialized
-    };
-
-    struct iovec asyncSafeToString(int n, AsyncSafeIntBuffer &&result = Qt::Uninitialized);
-#elif defined(Q_OS_WIN)
-    // Windows doesn't need to be async-safe
-    template <typename... Args> static void writeToStderr(Args &&... args)
-    {
-        (std::cerr << ... << args);
-    }
-
-    inline std::string asyncSafeToString(int n)
-    {
-        return std::to_string(n);
-    }
-#endif // defined(Q_OS_UNIX) && (!defined(Q_OS_WASM) || QT_CONFIG(thread))
-
     bool alreadyDebugging();
     void blockUnixSignals();
 
@@ -149,32 +109,6 @@ namespace CrashHandler {
         int setupAlternateStack();
         void freeAlternateStack();
 
-        template <typename T> static
-                std::enable_if_t<sizeof(std::declval<T>().si_pid) + sizeof(std::declval<T>().si_uid) >= 1>
-                printSentSignalInfo(T *info)
-        {
-            writeToStderr(" sent by PID ", asyncSafeToString(info->si_pid),
-                          " UID ", asyncSafeToString(info->si_uid));
-        }
-        static void printSentSignalInfo(...) {}
-
-        template <typename T> static
-                std::enable_if_t<sizeof(std::declval<T>().si_addr) >= 1> printCrashingSignalInfo(T *info)
-        {
-            using HexString = std::array<char, sizeof(quintptr) * 2>;
-            auto toHexString = [](quintptr u, HexString &&r = {}) {
-                int shift = sizeof(quintptr) * 8 - 4;
-                for (size_t i = 0; i < sizeof(quintptr) * 2; ++i, shift -= 4)
-                    r[i] = QtMiscUtils::toHexLower(u >> shift);
-                struct iovec vec;
-                vec.iov_base = r.data();
-                vec.iov_len = r.size();
-                return vec;
-            };
-            writeToStderr(", code ", asyncSafeToString(info->si_code),
-                          ", for address 0x", toHexString(quintptr(info->si_addr)));
-        }
-        static void printCrashingSignalInfo(...) {}
         static void actionHandler(int signum, siginfo_t *info, void * /* ucontext */);
 
         [[maybe_unused]] static void regularHandler(int signum)
diff --git a/src/testlib/qtestcrashhandler_unix.cpp b/src/testlib/qtestcrashhandler_unix.cpp
index f0ffe36dd66..86a77312ba4 100644
--- a/src/testlib/qtestcrashhandler_unix.cpp
+++ b/src/testlib/qtestcrashhandler_unix.cpp
@@ -68,21 +68,36 @@ QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
 
-namespace QTest {
-namespace CrashHandler {
-struct iovec IoVec(struct iovec vec)
+template <typename... Args> static ssize_t writeToStderr(Args &&... args)
 {
-    return vec;
-}
-struct iovec IoVec(const char *str)
-{
-    struct iovec r = {};
-    r.iov_base = const_cast<char *>(str);
-    r.iov_len = strlen(str);
-    return r;
+    auto makeIovec = [](auto &&arg) {
+        if constexpr (std::is_same_v<std::decay_t<decltype(arg)>, iovec>) {
+            return arg;
+        } else {
+            struct iovec r = {};
+            r.iov_base = const_cast<char *>(arg);
+            r.iov_len = strlen(arg);
+            return r;
+        }
+    };
+    struct iovec vec[] = { makeIovec(std::forward<Args>(args))... };
+    return ::writev(STDERR_FILENO, vec, std::size(vec));
 }
 
-struct iovec asyncSafeToString(int n, AsyncSafeIntBuffer &&result)
+namespace {
+// async-signal-safe conversion from int to string
+struct AsyncSafeIntBuffer
+{
+    // digits10 + 1 for all possible digits
+    // +1 for the sign
+    // +1 for the terminating null
+    static constexpr int Digits10 = std::numeric_limits<int>::digits10 + 3;
+    std::array<char, Digits10> array;
+    constexpr AsyncSafeIntBuffer() : array{} {}     // initializes array
+    AsyncSafeIntBuffer(Qt::Initialization) {}       // leaves array uninitialized
+};
+
+struct iovec asyncSafeToString(int n, AsyncSafeIntBuffer &&result = Qt::Uninitialized)
 {
     char *ptr = result.array.data();
     if (false) {
@@ -127,7 +142,10 @@ struct iovec asyncSafeToString(int n, AsyncSafeIntBuffer &&result)
     r.iov_len = ptr - result.array.data();
     return r;
 };
+} // unnamed namespace
 
+namespace QTest {
+namespace CrashHandler {
 bool alreadyDebugging()
 {
 #if defined(Q_OS_LINUX)
@@ -349,6 +367,33 @@ void blockUnixSignals()
     pthread_sigmask(SIG_BLOCK, &set, nullptr);
 }
 
+template <typename T> static
+        std::enable_if_t<sizeof(std::declval<T>().si_pid) + sizeof(std::declval<T>().si_uid) >= 1>
+printSentSignalInfo(T *info)
+{
+    writeToStderr(" sent by PID ", asyncSafeToString(info->si_pid),
+                  " UID ", asyncSafeToString(info->si_uid));
+}
+[[maybe_unused]] static void printSentSignalInfo(...) {}
+
+template <typename T> static std::enable_if_t<sizeof(std::declval<T>().si_addr) >= 1>
+printCrashingSignalInfo(T *info)
+{
+    using HexString = std::array<char, sizeof(quintptr) * 2>;
+    auto toHexString = [](quintptr u, HexString &&r = {}) {
+        int shift = sizeof(quintptr) * 8 - 4;
+        for (size_t i = 0; i < sizeof(quintptr) * 2; ++i, shift -= 4)
+            r[i] = QtMiscUtils::toHexLower(u >> shift);
+        struct iovec vec;
+        vec.iov_base = r.data();
+        vec.iov_len = r.size();
+        return vec;
+    };
+    writeToStderr(", code ", asyncSafeToString(info->si_code),
+                  ", for address 0x", toHexString(quintptr(info->si_addr)));
+}
+[[maybe_unused]] static void printCrashingSignalInfo(...) {}
+
 bool FatalSignalHandler::pauseOnCrash = false;
 
 FatalSignalHandler::FatalSignalHandler()
diff --git a/src/testlib/qtestcrashhandler_win.cpp b/src/testlib/qtestcrashhandler_win.cpp
index f814a6bc68e..6a9f610eabd 100644
--- a/src/testlib/qtestcrashhandler_win.cpp
+++ b/src/testlib/qtestcrashhandler_win.cpp
@@ -51,9 +51,11 @@ void printTestRunTime()
     const int msecsFunctionTime = qRound(QTestLog::msecsFunctionTime());
     const int msecsTotalTime = qRound(QTestLog::msecsTotalTime());
     const char *const name = QTest::currentTestFunction();
-    writeToStderr("\n         ", name ? name : "[Non-test]",
-                  " function time: ", asyncSafeToString(msecsFunctionTime),
-                  "ms, total time: ", asyncSafeToString(msecsTotalTime), "ms\n");
+
+    // Windows doesn't have the concept of async-safety, so fprintf() is
+    // probably as good as WriteFile() and WriteConsole().
+    fprintf(stderr, "\n         %s function time: %dms, total time: %dms\n",
+            name ? name : "[Non-test]", msecsFunctionTime, msecsTotalTime);
 }
 
 void generateStackTrace()