diff --git a/cockatrice/src/interface/deck_loader/deck_loader.cpp b/cockatrice/src/interface/deck_loader/deck_loader.cpp
index 9a58cf3f9..39a0c1071 100644
--- a/cockatrice/src/interface/deck_loader/deck_loader.cpp
+++ b/cockatrice/src/interface/deck_loader/deck_loader.cpp
@@ -458,51 +458,54 @@ bool DeckLoader::convertToCockatriceFormat(LoadedDeck &deck)
         return false;
     }
 
+    // Determine the format before touching any file, so an already-converted or
+    // unsupported deck never truncates or deletes anything.
+    switch (DeckFileFormat::getFormatFromName(fileName)) {
+        case DeckFileFormat::PlainText:
+            break;
+        case DeckFileFormat::Cockatrice:
+            qCInfo(DeckLoaderLog) << "File is already in Cockatrice format. No conversion needed.";
+            return true;
+        default:
+            qCWarning(DeckLoaderLog) << "Unsupported file format for conversion:" << fileName;
+            return false;
+    }
+
     // Change the file extension to .cod
     QFileInfo fileInfo(fileName);
     QString newFileName = QDir::toNativeSeparators(fileInfo.path() + "/" + fileInfo.completeBaseName() + ".cod");
 
-    // Open the new file for writing
-    QFile file(newFileName);
+    // Use QSaveFile so a failed write (e.g. a full disk) cannot leave a 0-byte .cod
+    // behind and then delete the original deck.
+    QSaveFile file(newFileName);
     if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
         qCWarning(DeckLoaderLog) << "Failed to open file for writing:" << newFileName;
         return false;
     }
 
-    bool result = false;
-
-    // Perform file modifications based on the detected format
-    switch (DeckFileFormat::getFormatFromName(fileName)) {
-        case DeckFileFormat::PlainText:
-            // Save in Cockatrice's native format
-            result = deck.deckList.saveToFile_Native(&file);
-            break;
-        case DeckFileFormat::Cockatrice:
-            qCInfo(DeckLoaderLog) << "File is already in Cockatrice format. No conversion needed.";
-            result = true;
-            break;
-        default:
-            qCWarning(DeckLoaderLog) << "Unsupported file format for conversion:" << fileName;
-            result = false;
-            break;
+    if (!deck.deckList.saveToFile_Native(&file)) {
+        file.cancelWriting();
+        qCWarning(DeckLoaderLog) << "Failed to serialize deck for file:" << newFileName;
+        return false;
     }
 
-    file.close();
-
-    // Delete the old file if conversion was successful
-    if (result) {
-        if (!QFile::remove(fileName)) {
-            qCWarning(DeckLoaderLog) << "Failed to delete original file:" << fileName;
-        } else {
-            qCInfo(DeckLoaderLog) << "Original file deleted successfully:" << fileName;
-        }
-        deck.lastLoadInfo = {
-            .fileName = newFileName,
-            .fileFormat = DeckFileFormat::Cockatrice,
-        };
+    if (!file.commit()) {
+        qCWarning(DeckLoaderLog) << "Failed to convert deck to " << newFileName << ":" << file.errorString();
+        return false;
     }
 
-    return result;
+    // Conversion succeeded: delete the original file.
+    if (!QFile::remove(fileName)) {
+        qCWarning(DeckLoaderLog) << "Failed to delete original file:" << fileName;
+    } else {
+        qCInfo(DeckLoaderLog) << "Original file deleted successfully:" << fileName;
+    }
+    deck.lastLoadInfo = {
+        .fileName = newFileName,
+        .fileFormat = DeckFileFormat::Cockatrice,
+    };
+
+    return true;
 }
 
 void DeckLoader::printDeckListNode(QTextCursor *cursor, const InnerDecklistNode *node)