Index: /trunk/src/org/openstreetmap/josm/gui/layer/AbstractTileSourceLayer.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/layer/AbstractTileSourceLayer.java	(revision 11946)
+++ /trunk/src/org/openstreetmap/josm/gui/layer/AbstractTileSourceLayer.java	(revision 11947)
@@ -412,5 +412,11 @@
          */
         int intResult = (int) Math.round(result + 1 + ZOOM_OFFSET.get() / 1.9);
-        intResult = Utils.clamp(intResult, getMinZoomLvl(), getMaxZoomLvl());
+        int minZoom = getMinZoomLvl();
+        int maxZoom = getMaxZoomLvl();
+        if (minZoom <= maxZoom) {
+            intResult = Utils.clamp(intResult, minZoom, maxZoom);
+        } else if (intResult > maxZoom) {
+            intResult = maxZoom;
+        }
         return intResult;
     }