diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index 53019e1ff4..51a574987e 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -833,7 +833,7 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
                 // In buffered mode, we try to fill up the QIODevice buffer before
                 // we do anything else.
                 // buffer is empty at this point, try to fill it
-                int bytesToBuffer = QIODEVICE_BUFFERSIZE;
+                const int bytesToBuffer = QIODEVICE_BUFFERSIZE;
                 char *writePointer = d->buffer.reserve(bytesToBuffer);
 
                 // Make sure the device is positioned correctly.
@@ -1013,6 +1013,8 @@ QByteArray QIODevice::readAll()
 
     // flush internal read buffer
     if (!(d->openMode & Text) && !d->buffer.isEmpty()) {
+        if (d->buffer.size() >= INT_MAX)
+            return QByteArray();
         result = d->buffer.readAll();
         readBytes = result.size();
         d->pos += readBytes;
@@ -1031,6 +1033,8 @@ QByteArray QIODevice::readAll()
     } else {
         // Read it all in one go.
         // If resize fails, don't read anything.
+        if (readBytes + theSize - d->pos > INT_MAX)
+            return QByteArray();
         result.resize(int(readBytes + theSize - d->pos));
         readBytes += read(result.data() + readBytes, result.size() - readBytes);
     }
diff --git a/src/corelib/io/qiodevice_p.h b/src/corelib/io/qiodevice_p.h
index faf64e2cf1..132ab1cad2 100644
--- a/src/corelib/io/qiodevice_p.h
+++ b/src/corelib/io/qiodevice_p.h
@@ -84,13 +84,13 @@ public:
         first = buf;
         capacity = 0;
     }
-    int size() const {
+    qint64 size() const {
         return len;
     }
     bool isEmpty() const {
         return len == 0;
     }
-    void skip(int n) {
+    void skip(qint64 n) {
         if (n >= len) {
             clear();
         } else {
@@ -106,14 +106,14 @@ public:
         first++;
         return ch;
     }
-    int read(char* target, int size) {
+    int read(char* target, qint64 size) {
         int r = qMin(size, len);
         memcpy(target, first, r);
         len -= r;
         first += r;
         return r;
     }
-    int peek(char* target, int size) {
+    int peek(char* target, qint64 size) {
         int r = qMin(size, len);
         memcpy(target, first, r);
         return r;
@@ -124,7 +124,7 @@ public:
         len += size;
         return writePtr;
     }
-    void chop(int size) {
+    void chop(qint64 size) {
         if (size >= len) {
             clear();
         } else {
@@ -136,7 +136,7 @@ public:
         clear();
         return retVal;
     }
-    int readLine(char* target, int size) {
+    int readLine(char* target, qint64 size) {
         int r = qMin(size, len);
         char* eol = static_cast<char*>(memchr(first, '\n', r));
         if (eol)
@@ -158,7 +158,7 @@ public:
         len++;
         *first = c;
     }
-    void ungetBlock(const char* block, int size) {
+    void ungetBlock(const char* block, qint64 size) {
         if ((first - buf) < size) {
             // underflow, the existing valid data needs to move to the end of the (potentially bigger) buffer
             makeSpace(len + size, freeSpaceAtStart);
@@ -191,7 +191,7 @@ private:
 
 private:
     // length of the unread data
-    int len;
+    qint64 len;
     // start of the unread data
     char* first;
     // the allocated buffer