diff --git a/bigtext.py b/bigtext.py
index 089d13d..0b28301 100644
--- a/bigtext.py
+++ b/bigtext.py
@@ -178,7 +178,13 @@ class InnerBigText(QWidget):
         self.parent.v_scroll_bar.setValue(self._byte_offset)
 
     def mousePressEvent(self, e: QtGui.QMouseEvent) -> None:
-        if e.buttons() == Qt.MouseButton.LeftButton:
+        if e.buttons() == Qt.MouseButton.LeftButton and e.modifiers() == Qt.KeyboardModifier.ShiftModifier:
+            offset = self.to_byte_offset(e)
+            self.selection_highlight.set_end_byte(offset)
+            self.update()
+            return
+
+        if e.buttons() == Qt.MouseButton.LeftButton and e.modifiers() == Qt.KeyboardModifier.NoModifier:
             offset = self.to_byte_offset(e)
             self.selection_highlight.set_start(offset)
             self.selection_highlight.set_end_byte(offset)