diff --git a/src/imageformats/pcx.cpp b/src/imageformats/pcx.cpp
index 4efd19a..c707e3b 100644
--- a/src/imageformats/pcx.cpp
+++ b/src/imageformats/pcx.cpp
@@ -266,29 +266,30 @@ PCXHEADER::PCXHEADER()
 
 bool peekHeader(QIODevice *d, PCXHEADER& h)
 {
-    qint64 pos = 0;
-    if (!d->isSequential()) {
-        pos = d->pos();
+    qint64 oldPos = d->pos();
+    QByteArray head = d->read(sizeof(PCXHEADER));
+    int readBytes = head.size();
+
+    if (d->isSequential()) {
+        for (int pos = readBytes -1; pos >= 0; --pos) {
+            d->ungetChar(head[pos]);
+        }
+    } else {
+        d->seek(oldPos);
+    }
+
+    if (readBytes < sizeof(PCXHEADER)) {
+        return false;
     }
 
     auto ok = false;
     { // datastream is destroyed before working on device
-        QDataStream ds(d);
+        QDataStream ds(head);
         ds.setByteOrder(QDataStream::LittleEndian);
         ds >> h;
         ok = ds.status() == QDataStream::Ok && h.isValid();
     }
 
-    if (!d->isSequential()) {
-        return d->seek(pos) && ok;
-    }
-
-    // sequential device undo
-    auto head = reinterpret_cast<char*>(&h);
-    auto readBytes = sizeof(h);
-    while (readBytes > 0) {
-        d->ungetChar(head[readBytes-- - 1]);
-    }
     return ok;
 }