diff --git a/data/core.yaml b/data/core.yaml
index e94fbb51d..8eba17daf 100644
--- a/data/core.yaml
+++ b/data/core.yaml
@@ -100,6 +100,7 @@ en:
       too_large: This can't be made circular because not enough of it is currently visible.
       connected_to_hidden: This can't be made circular because it is connected to a hidden feature.
       not_downloaded: This can't be made circular because parts of it have not yet been downloaded.
+      already_circular: This can't be made circular because it's already circular.
     orthogonalize:
       title: Square
       description:
diff --git a/modules/actions/circularize.js b/modules/actions/circularize.js
index b7f8b4682..b388ec52b 100644
--- a/modules/actions/circularize.js
+++ b/modules/actions/circularize.js
@@ -9,6 +9,7 @@ import {
 import { geoVecInterp, geoVecLength } from '../geo';
 import { osmNode } from '../osm/node';
 import { utilArrayUniq } from '../util';
+import { geoVecLengthSquare } from '../geo/vector';
 
 
 export function actionCircularize(wayId, projection, maxAngle) {
@@ -228,6 +229,49 @@ export function actionCircularize(wayId, projection, maxAngle) {
         if (!graph.entity(wayId).isClosed()) {
             return 'not_closed';
         }
+
+        //disable when already circular
+        var way = graph.entity(wayId);
+        var nodes = utilArrayUniq(graph.childNodes(way));
+        var points = nodes.map(function(n) { return projection(n.loc); });
+        var hull = d3_polygonHull(points);
+        var epsilonAngle =  Math.PI / 180;
+        if (hull.length !== points.length || hull.length < 3){
+            return false;
+        }
+        var centroid = d3_polygonCentroid(points);
+        var radius = geoVecLengthSquare(centroid, points[0]);
+
+        // compare distances between centroid and points
+        for (var i = 0; i<hull.length; i++){
+            var actualPoint = hull[i];
+            var actualDist = geoVecLengthSquare(actualPoint, centroid);
+            var diff = Math.abs(actualDist - radius);
+            //compare distances with epsilon-error (5%)
+            if (diff > 0.05*radius) {
+                return false;
+            }
+        }
+        
+        //check if central angles are smaller than maxAngle
+        for (i = 0; i<hull.length; i++){
+            actualPoint = hull[i];
+            var nextPoint = hull[(i+1)%hull.length];
+            var startAngle = Math.atan2(actualPoint[1] - centroid[1], actualPoint[0] - centroid[0]);
+            var endAngle = Math.atan2(nextPoint[1] - centroid[1], nextPoint[0] - centroid[0]);
+            var angle = endAngle - startAngle;
+            if (angle < 0) {
+                angle = -angle;
+            }
+            if (angle > Math.PI){
+                angle = (2*Math.PI - angle);
+            }
+ 
+            if (angle > maxAngle + epsilonAngle) {
+                return false;
+            }
+        }
+        return 'already_circular';
     };
 
 
diff --git a/modules/geo/index.js b/modules/geo/index.js
index 88402d97a..609e9c8a9 100644
--- a/modules/geo/index.js
+++ b/modules/geo/index.js
@@ -37,6 +37,7 @@ export { geoVecEqual } from './vector.js';
 export { geoVecFloor } from './vector.js';
 export { geoVecInterp } from './vector.js';
 export { geoVecLength } from './vector.js';
+export { geoVecLengthSquare } from '/vector.js';
 export { geoVecNormalize } from './vector.js';
 export { geoVecNormalizedDot } from './vector.js';
 export { geoVecProject } from './vector.js';
diff --git a/modules/geo/vector.js b/modules/geo/vector.js
index 97318607d..8dade4393 100644
--- a/modules/geo/vector.js
+++ b/modules/geo/vector.js
@@ -37,10 +37,15 @@ export function geoVecInterp(a, b, t) {
 
 // http://jsperf.com/id-dist-optimization
 export function geoVecLength(a, b) {
+    return Math.sqrt(geoVecLengthSquare(a,b));
+}
+
+// length of vector raised to the power two
+export function geoVecLengthSquare(a, b) {
     b = b || [0, 0];
     var x = a[0] - b[0];
     var y = a[1] - b[1];
-    return Math.sqrt((x * x) + (y * y));
+    return (x * x) + (y * y);
 }
 
 // get a unit vector
diff --git a/test/spec/actions/circularize.js b/test/spec/actions/circularize.js
index e20b268fe..c6c0f9813 100644
--- a/test/spec/actions/circularize.js
+++ b/test/spec/actions/circularize.js
@@ -288,6 +288,33 @@ describe('iD.actionCircularize', function () {
         expect(isCircular('-', graph)).to.be.ok;
     });
 
+    it('not disable circularize when its not circular', function(){
+        var graph = iD.coreGraph([
+            iD.osmNode({id: 'a', loc: [0, 0]}),
+            iD.osmNode({id: 'b', loc: [2, 0]}),
+            iD.osmNode({id: 'c', loc: [2, 2]}),
+            iD.osmNode({id: 'd', loc: [0, 2]}),
+            iD.osmWay({id: '-', nodes: ['a', 'b', 'c', 'd', 'a']})
+        ]);
+        var result = iD.actionCircularize('-', projection).disabled(graph);
+        expect(result).to.be.false;
+
+    });
+
+    it('disable circularize twice', function(){
+        var graph = iD.coreGraph([
+            iD.osmNode({id: 'a', loc: [0, 0]}),
+            iD.osmNode({id: 'b', loc: [2, 0]}),
+            iD.osmNode({id: 'c', loc: [2, 2]}),
+            iD.osmNode({id: 'd', loc: [0, 2]}),
+            iD.osmWay({id: '-', nodes: ['a', 'b', 'c', 'd', 'a']})
+        ]);
+        graph = iD.actionCircularize('-', projection)(graph);
+        var result = iD.actionCircularize('-', projection).disabled(graph);
+        expect(result).to.eql('already_circular');
+
+    });
+
 
     describe('transitions', function () {
         it('is transitionable', function() {