diff --git a/lib/OpenLayers/BaseTypes/LonLat.js b/lib/OpenLayers/BaseTypes/LonLat.js
index fed3f09b04..33f637253a 100644
--- a/lib/OpenLayers/BaseTypes/LonLat.js
+++ b/lib/OpenLayers/BaseTypes/LonLat.js
@@ -92,7 +92,8 @@ OpenLayers.LonLat = OpenLayers.Class({
             OpenLayers.Console.error(msg);
             return null;
         }
-        return new OpenLayers.LonLat(this.lon + lon, this.lat + lat);
+        return new OpenLayers.LonLat(this.lon + OpenLayers.Util.toFloat(lon), 
+                                     this.lat + OpenLayers.Util.toFloat(lat));
     },
 
     /** 
diff --git a/tests/BaseTypes/LonLat.html b/tests/BaseTypes/LonLat.html
index 0d244fa80f..400d30b409 100644
--- a/tests/BaseTypes/LonLat.html
+++ b/tests/BaseTypes/LonLat.html
@@ -52,7 +52,7 @@
     }
 
     function test_LonLat_add(t) {
-        t.plan( 8 );
+        t.plan(10);
 
         origLL = new OpenLayers.LonLat(10,100);
         lonlatA = origLL.clone();
@@ -76,6 +76,11 @@
         addpx = lonlatA.add(5, null);
         t.ok( lonlatA.equals(origLL), "lonlatA is not modified by erroneous add operation (null lat)");
         t.ok(addpx == null, "returns null on erroneous add operation (null lat)");
+
+        // string values
+        addpx = origLL.clone().add("5", "50");
+        t.eq(addpx.lon, 15, "addpx.lon is set correctly");
+        t.eq(addpx.lat, 150, "addpx.lat is set correctly");
     }
     
     function test_LonLat_equals(t) {