diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 7f1d5dd..15d014c 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -1302,6 +1302,40 @@ QRect QXcbWindow::windowToWmGeometry(QRect r) const
         r.translate(m_frameMargins.left(), m_frameMargins.top());
     } else if (!frameInclusive && m_gravity == XCB_GRAVITY_NORTH_WEST) {
         r.translate(-m_frameMargins.left(), -m_frameMargins.top());
+    } else if (m_gravity == XCB_GRAVITY_CENTER) {
+        if (frameInclusive) {
+            // r describes the *position* of the window frame and the *size* of
+            // our own window. Yes, this is a weird QRect. Blame
+            // QWindow::setFramePosition().
+            //
+            // The center of the frame is at:
+            //   r.topLeft() + frame_size/2
+            // = r.topLeft() + (r.size() + QSize(left+right, top+bottom))/2
+            //
+            // The returned rect should have a position pos whose center will be:
+            //   pos.topLeft() + pos.size()/2    (This is just as below)
+            // = pos.topLeft() + r.size()/2
+            //
+            // Since those two centers are equal, we can calculate pos.topLeft:
+            //   pos.topLeft() = r.topLeft() + QSize(left+right, top+bottom)/2
+            r.translate((m_frameMargins.left() + m_frameMargins.right())/2,
+                        (m_frameMargins.top()  + m_frameMargins.bottom())/2);
+        } else {
+            // The frame's center will be at:
+            //   frame.topLeft() + frame.size()/2
+            // = (r.topLeft() - QSize(left, top)) + frame.size()/2
+            // = (r.topLeft() - QSize(left, top)) + (r.size() + QSize(left+right, top+bottom))/2
+            // = r.topLeft() + (r.size() + QSize(right-left, bottom-top))/2
+            //
+            // The returned rect should have a position pos whose center will be:
+            //   pos.topLeft() + pos.size()/2    (This is just as above)
+            // = pos.topLeft() + r.size()/2
+            //
+            // Again, those two centers are equal and we end up with:
+            //   pos.topLeft() = r.topLeft() + QSize(right-left, bottom-top)/2
+            r.translate((m_frameMargins.right()  - m_frameMargins.left())/2,
+                        (m_frameMargins.bottom() - m_frameMargins.top())/2);
+        }
     }
     return r;
 }