diff --git a/qwt/plot_canvas.py b/qwt/plot_canvas.py
index c7c7950..1b90ed1 100644
--- a/qwt/plot_canvas.py
+++ b/qwt/plot_canvas.py
@@ -13,7 +13,7 @@
    :members:
 """
 
-import os
+from collections.abc import Sequence
 
 from qtpy.QtCore import QEvent, QObject, QPoint, QPointF, QRect, QRectF, QSize, Qt
 from qtpy.QtGui import (
@@ -34,8 +34,6 @@
 from qwt.null_paintdevice import QwtNullPaintDevice
 from qwt.painter import QwtPainter
 
-QT_API = os.environ["QT_API"]
-
 
 class Border(object):
     def __init__(self):
@@ -71,17 +69,15 @@ def updateState(self, state):
             self.__origin = state.brushOrigin()
 
     def drawRects(self, rects, count):
-        if QT_API.startswith("pyside"):
-            # Pyside
-            if isinstance(rects, (QRect, QRectF)):
-                self.border.list = [rects]
-            else:
-                for i in range(count):
-                    self.border.rectList += [rects.getRect().index(i)]
+        if isinstance(rects, (QRect, QRectF)):
+            self.border.rectList = [QRectF(rects)]
+        elif isinstance(rects, Sequence):
+            self.border.rectList.extend(QRectF(rects[i]) for i in range(count))
         else:
-            # PyQt
-            for i in range(count):
-                self.border.rectList += [rects[i]]
+            raise TypeError(
+                "drawRects() expects a QRect, QRectF or a sequence of them, "
+                f"but got {type(rects).__name__}"
+            )
 
     def drawPath(self, path):
         rect = QRectF(QPointF(0.0, 0.0), self.__size)