diff --git a/lib/OpenLayers/Layer.js b/lib/OpenLayers/Layer.js
index 8ae093513c..ac81a86c59 100644
--- a/lib/OpenLayers/Layer.js
+++ b/lib/OpenLayers/Layer.js
@@ -952,7 +952,7 @@ OpenLayers.Layer = OpenLayers.Class({
         if(this.map.fractionalZoom) {
             var low = Math.floor(zoom);
             var high = Math.ceil(zoom);
-            resolution = this.resolutions[high] +
+            resolution = this.resolutions[low] -
                 ((zoom-low) * (this.resolutions[low]-this.resolutions[high]));
         } else {
             resolution = this.resolutions[Math.round(zoom)];
@@ -1000,7 +1000,7 @@ OpenLayers.Layer = OpenLayers.Class({
             }
             var dRes = highRes - lowRes;
             if(dRes > 0) {
-                zoom = lowZoom + ((resolution - lowRes) / dRes);
+                zoom = lowZoom + ((highRes - resolution) / dRes);
             } else {
                 zoom = lowZoom;
             }
diff --git a/tests/Layer.html b/tests/Layer.html
index 7e0fb9a136..f86490be9d 100644
--- a/tests/Layer.html
+++ b/tests/Layer.html
@@ -414,7 +414,7 @@
     }
     
     function test_Layer_getResolutionForZoom(t) {
-        t.plan(5);
+        t.plan(8);
         var layer = new OpenLayers.Layer("test");
         layer.map = {fractionalZoom: false};
         layer.resolutions = ["zero", "one", "two"];
@@ -427,6 +427,16 @@
         layer.map.fractionalZoom = true;
         t.eq(layer.getResolutionForZoom(1).toPrecision(6), (4).toPrecision(6),
              "(fractionalZoom true) returns resolution for integer zoom");
+
+        t.eq(layer.getResolutionForZoom(1.3).toPrecision(6), (4.6).toPrecision(6),
+             "(fractionalZoom true) for zoom 1.3 should be 4.6");
+
+        t.eq(layer.getResolutionForZoom(1.6).toPrecision(6), (5.2).toPrecision(6),
+             "(fractionalZoom true) for zoom 1.6 should be 5.2");
+
+        t.eq(layer.getResolutionForZoom(1.8).toPrecision(6), (5.6).toPrecision(6),
+             "(fractionalZoom true) for zoom 1.8 should be 5.6");
+
         t.eq(layer.getResolutionForZoom(1.5).toPrecision(6), (5).toPrecision(6),
              "(fractionalZoom true) returns resolution for float zoom");             
         t.eq(layer.getResolutionForZoom(3.5).toPrecision(6), (8).toPrecision(6),