diff --git a/src/corelib/io/qprocess_p.h b/src/corelib/io/qprocess_p.h
index c0273aeeaef..dacf41b77aa 100644
--- a/src/corelib/io/qprocess_p.h
+++ b/src/corelib/io/qprocess_p.h
@@ -303,7 +303,7 @@ public:
     void startProcess();
 #if defined(Q_OS_UNIX)
     void commitChannels() const;
-    void execChild(int workingDirectory, char **argv, char **envp) const;
+    void execChild(int workingDirectory, char **argv, char **envp) const noexcept;
 #endif
     bool processStarted(QString *errorMessage = nullptr);
     void processFinished();
diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index 5c72a39911a..d16fa7498e2 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -47,8 +47,40 @@
 
 QT_BEGIN_NAMESPACE
 
+// we need an errno number to use to indicate the child process modifier threw,
+// something the regular operations shouldn't set.
+static constexpr int FakeErrnoForThrow =
+#ifdef ECANCELED
+        ECANCELED
+#else
+        ESHUTDOWN
+#endif
+        ;
+
 using namespace Qt::StringLiterals;
 
+namespace {
+struct PThreadCancelGuard
+{
+#if defined(PTHREAD_CANCEL_DISABLE)
+    int oldstate;
+    PThreadCancelGuard() noexcept(false)
+    {
+        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
+    }
+    ~PThreadCancelGuard() noexcept(false)
+    {
+        reenable();
+    }
+    void reenable() noexcept(false)
+    {
+        // this doesn't touch errno
+        pthread_setcancelstate(oldstate, nullptr);
+    }
+#endif
+};
+}
+
 #if !defined(Q_OS_DARWIN)
 
 QT_BEGIN_INCLUDE_NAMESPACE
@@ -472,6 +504,11 @@ void QProcessPrivate::startProcess()
     const CharPointerList argv(resolveExecutable(program), arguments);
     const CharPointerList envp(environment.d.constData());
 
+    // Disable PThread cancellation from this point on: we mustn't have it
+    // enabled when the child starts running nor while our state could get
+    // corrupted if we abruptly exited this function.
+    PThreadCancelGuard cancelGuard;
+
     // Start the child.
     auto execChild1 = [this, workingDirFd, &argv, &envp]() {
         execChild(workingDirFd, argv.pointers.get(), envp.pointers.get());
@@ -539,12 +576,24 @@ void QProcessPrivate::startProcess()
         ::fcntl(stderrChannel.pipe[0], F_SETFL, ::fcntl(stderrChannel.pipe[0], F_GETFL) | O_NONBLOCK);
 }
 
+static bool callChildProcessModifier(const QProcessPrivate::UnixExtras *unixExtras) noexcept
+{
+    QT_TRY {
+        if (unixExtras->childProcessModifier)
+            unixExtras->childProcessModifier();
+    } QT_CATCH (...) {
+        errno = FakeErrnoForThrow;
+        return false;
+    }
+    return true;
+}
+
 // IMPORTANT:
 //
 // This function is called in a vfork() context on some OSes (notably, Linux
 // with forkfd), so it MUST NOT modify any non-local variable because it's
 // still sharing memory with the parent process.
-void QProcessPrivate::execChild(int workingDir, char **argv, char **envp) const
+void QProcessPrivate::execChild(int workingDir, char **argv, char **envp) const noexcept
 {
     ::signal(SIGPIPE, SIG_DFL);         // reset the signal that we ignored
 
@@ -564,8 +613,10 @@ void QProcessPrivate::execChild(int workingDir, char **argv, char **envp) const
     }
 
     if (unixExtras) {
-        if (unixExtras->childProcessModifier)
-            unixExtras->childProcessModifier();
+        if (!callChildProcessModifier(unixExtras.get())) {
+            std::strcpy(error.function, "throw");
+            goto report_errno;
+        }
     }
 
     // execute the process
@@ -965,6 +1016,9 @@ bool QProcessPrivate::startDetached(qint64 *pid)
     const CharPointerList argv(resolveExecutable(program), arguments);
     const CharPointerList envp(environment.d.constData());
 
+    // see startProcess() for more information
+    PThreadCancelGuard cancelGuard;
+
     pid_t childPid = fork();
     if (childPid == 0) {
         ::signal(SIGPIPE, SIG_DFL);     // reset the signal that we ignored
diff --git a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
index 4d54e8db27f..d10c9ea5662 100644
--- a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
+++ b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
@@ -112,6 +112,7 @@ private slots:
 #endif // Q_OS_WIN
 #if defined(Q_OS_UNIX)
     void setChildProcessModifier();
+    void throwInChildProcessModifier();
 #endif
     void exitCodeTest();
     void systemEnvironment();
@@ -1469,6 +1470,34 @@ void tst_QProcess::setChildProcessModifier()
     QCOMPARE(process.exitStatus(), QProcess::NormalExit);
     QCOMPARE(process.exitCode(), 0);
 }
+
+void tst_QProcess::throwInChildProcessModifier()
+{
+#ifndef __cpp_exceptions
+    Q_SKIP("Exceptions disabled.");
+#else
+    QProcess process;
+    process.setChildProcessModifier([]() {
+        throw 42;
+    });
+    process.setProgram("testProcessNormal/testProcessNormal");
+
+    process.start();
+    QVERIFY(!process.waitForStarted(5000));
+    QCOMPARE(process.state(), QProcess::NotRunning);
+    QCOMPARE(process.error(), QProcess::FailedToStart);
+    QVERIFY2(process.errorString().contains("throw"),
+             qPrintable(process.errorString()));
+
+    // try again, to ensure QProcess internal state wasn't corrupted
+    process.start();
+    QVERIFY(!process.waitForStarted(5000));
+    QCOMPARE(process.state(), QProcess::NotRunning);
+    QCOMPARE(process.error(), QProcess::FailedToStart);
+    QVERIFY2(process.errorString().contains("throw"),
+             qPrintable(process.errorString()));
+#endif
+}
 #endif
 
 void tst_QProcess::exitCodeTest()