diff --git a/bigtext.py b/bigtext.py
index 36cc01a..0c7d5fa 100644
--- a/bigtext.py
+++ b/bigtext.py
@@ -12,6 +12,7 @@ from PyQt6.QtGui import QMouseEvent
 from PyQt6.QtWidgets import *
 
 from ScaledScrollBar import ScaledScrollBar
+from conversion import humanbytes
 from highlight import Highlight
 from highlight_regex import HighlightRegex
 from highlight_selection import HighlightSelection
@@ -227,6 +228,20 @@ class InnerBigText(QWidget):
         if self.selection_highlight.start_byte != self.selection_highlight.end_byte:
             start = min(self.selection_highlight.start_byte, self.selection_highlight.end_byte)
             end = max(self.selection_highlight.start_byte, self.selection_highlight.end_byte)
+            if end - start > (1024 ** 2) * 5:
+                you_sure = QMessageBox(
+                    QMessageBox.Icon.Warning,
+                    self.tr("copy to clipboard"),
+                    self.tr(
+                        "You are about to copy <b>%s</b> to the clipboard. Are you sure you want to do that?" % humanbytes(
+                            end - start)))
+                you_sure.setStandardButtons(QMessageBox.StandardButton.Yes | QMessageBox.StandardButton.No)
+                you_sure.setDefaultButton(QMessageBox.StandardButton.No)
+                result = you_sure.exec()
+                if result != QMessageBox.StandardButton.Yes:
+                    # abort
+                    return
+
             selected_text = self.model.read_range(start, end)
             cb = QApplication.clipboard()
             cb.setText(selected_text)
diff --git a/conversion.py b/conversion.py
new file mode 100644
index 0000000..ff8009b
--- /dev/null
+++ b/conversion.py
@@ -0,0 +1,30 @@
+import unittest
+
+
+def humanbytes(bytes: int) -> str:
+    """non-localized conversion of bytes to human readable strings"""
+    powers = {0: 'bytes', 1: 'KB', 2: 'MB', 3: 'GB', 4: 'TB', 5: 'PB', 6: 'EB'}
+    power = 1
+    result = "%d bytes" % bytes
+    while bytes >= 1024 ** power and power in powers:
+        result = "%.3f" % (bytes / (1024 ** power))
+        result = result.rstrip("0")
+        result = result.rstrip(".")
+        result = result + " " + powers[power]
+        power = power + 1
+    return result
+
+
+class TestLogFileModel(unittest.TestCase):
+
+    def test_humanbytes(self):
+        inputs = {
+            0: "0 bytes",
+            1023: "1023 bytes",
+            1024: "1 KB",
+            1048575: "1023.999 KB",
+            1048576: "1 MB",
+        }
+        for input in inputs.keys():
+            actual = humanbytes(input)
+            self.assertEqual(inputs[input], actual)