diff --git a/src/concurrent/qtconcurrentiteratekernel.cpp b/src/concurrent/qtconcurrentiteratekernel.cpp
index 088c8384ced..00228f181cb 100644
--- a/src/concurrent/qtconcurrentiteratekernel.cpp
+++ b/src/concurrent/qtconcurrentiteratekernel.cpp
@@ -67,7 +67,7 @@ namespace QtConcurrent {
 
 */
 BlockSizeManager::BlockSizeManager(QThreadPool *pool, int iterationCount)
-    : maxBlockSize(iterationCount / (pool->maxThreadCount() * 2)),
+    : maxBlockSize(iterationCount / (std::max(pool->maxThreadCount(), 1) * 2)),
       beforeUser(0), afterUser(0),
       m_blockSize(1)
 { }
diff --git a/src/concurrent/qtconcurrentreducekernel.h b/src/concurrent/qtconcurrentreducekernel.h
index cb7d7910aad..c337a9192fc 100644
--- a/src/concurrent/qtconcurrentreducekernel.h
+++ b/src/concurrent/qtconcurrentreducekernel.h
@@ -117,7 +117,7 @@ class ReduceKernel
 public:
     ReduceKernel(QThreadPool *pool, ReduceOptions _reduceOptions)
         : reduceOptions(_reduceOptions), progress(0), resultsMapSize(0),
-          threadCount(pool->maxThreadCount())
+          threadCount(std::max(pool->maxThreadCount(), 1))
     { }
 
     void runReduce(ReduceFunctor &reduce,
diff --git a/src/network/kernel/qhostinfo.cpp b/src/network/kernel/qhostinfo.cpp
index e7df47da6f2..2c6443b0ea3 100644
--- a/src/network/kernel/qhostinfo.cpp
+++ b/src/network/kernel/qhostinfo.cpp
@@ -965,7 +965,7 @@ void QHostInfoLookupManager::rescheduleWithMutexHeld()
                                        isAlreadyRunning).second,
                            scheduledLookups.end());
 
-    const int availableThreads = threadPool.maxThreadCount() - currentLookups.size();
+    const int availableThreads = std::max(threadPool.maxThreadCount(), 1) - currentLookups.size();
     if (availableThreads > 0) {
         int readyToStartCount = qMin(availableThreads, scheduledLookups.size());
         auto it = scheduledLookups.begin();
diff --git a/tests/auto/concurrent/qtconcurrentmap/tst_qtconcurrentmap.cpp b/tests/auto/concurrent/qtconcurrentmap/tst_qtconcurrentmap.cpp
index 94248404da4..e66edb1b602 100644
--- a/tests/auto/concurrent/qtconcurrentmap/tst_qtconcurrentmap.cpp
+++ b/tests/auto/concurrent/qtconcurrentmap/tst_qtconcurrentmap.cpp
@@ -185,6 +185,17 @@ void tst_QtConcurrentMap::map()
         QCOMPARE(list, NonTemplateSequence({ 2, 4, 6 }));
     }
 
+    // custom pool with invalid number of threads
+    {
+        QList<int> list;
+        list << 1 << 2 << 3;
+        QThreadPool pool;
+        pool.setMaxThreadCount(0); // explicitly set incorrect value
+        // This should not crash
+        QtConcurrent::map(&pool, list, MultiplyBy2InPlace()).waitForFinished();
+        QCOMPARE(list, QList<int>() << 2 << 4 << 6);
+    }
+
 #if 0
     // not allowed: map() with immutable sequences makes no sense
     {
@@ -1075,6 +1086,17 @@ void tst_QtConcurrentMap::mappedReducedThreadPool()
                                                           intCube, intSumReduce);
         QCOMPARE(result, sumOfCubes);
     }
+
+    {
+        // pool with invalid number of threads
+        QThreadPool pool;
+        pool.setMaxThreadCount(0); // explicitly set incorrect value
+
+        // This should not crash
+        NonTemplateSequence list { 1, 2, 3 };
+        auto future = QtConcurrent::mappedReduced(&pool, list, multiplyBy2, intSumReduce);
+        QCOMPARE(future.result(), 12);
+    }
 }
 
 void tst_QtConcurrentMap::mappedReducedWithMoveOnlyCallable()