diff --git a/js/id/actions/straighten.js b/js/id/actions/straighten.js
index 3f61fb825..ea0190cb0 100644
--- a/js/id/actions/straighten.js
+++ b/js/id/actions/straighten.js
@@ -45,7 +45,7 @@ iD.actions.Straighten = function(wayId, projection) {
 
         return graph;
     };
-    
+
     action.disabled = function(graph) {
         // check way isn't too bendy
         var way = graph.entity(wayId),
@@ -56,6 +56,10 @@ iD.actions.Straighten = function(wayId, projection) {
             threshold = 0.2 * Math.sqrt(Math.pow(startPoint[0] - endPoint[0], 2) + Math.pow(startPoint[1] - endPoint[1], 2)),
             i;
 
+        if (threshold === 0) {
+            return 'too_bendy';
+        }
+
         for (i = 1; i < points.length-1; i++) {
             var point = points[i],
                 u = positionAlongWay(point, startPoint, endPoint),
@@ -64,7 +68,7 @@ iD.actions.Straighten = function(wayId, projection) {
                 dist = Math.sqrt(Math.pow(p0 - point[0], 2) + Math.pow(p1 - point[1], 2));
 
             // to bendy if point is off by 20% of total start/end distance in projected space
-            if (dist > threshold) {
+            if (isNaN(dist) || dist > threshold) {
                 return 'too_bendy';
             }
         }
diff --git a/test/spec/actions/straighten.js b/test/spec/actions/straighten.js
index 8f43683c6..b373a5e89 100644
--- a/test/spec/actions/straighten.js
+++ b/test/spec/actions/straighten.js
@@ -1,6 +1,44 @@
 describe("iD.actions.Straighten", function () {
     var projection = d3.geo.mercator();
 
+    describe("#disabled", function () {
+        it("returns falsy for ways with internal nodes near centerline", function () {
+            var graph = iD.Graph([
+                iD.Node({id: 'a', loc: [0, 0]}),
+                iD.Node({id: 'b', loc: [1, 0.1]}),
+                iD.Node({id: 'c', loc: [2, 0]}),
+                iD.Node({id: 'd', loc: [3, 0]}),
+                iD.Way({id: '-', nodes: ['a', 'b', 'c', 'd']})
+            ]);
+
+            expect(iD.actions.Straighten('-', projection).disabled(graph)).not.to.be.ok;
+        });
+
+        it("returns 'too_bendy' for ways with internal nodes far off centerline", function () {
+            var graph = iD.Graph([
+                iD.Node({id: 'a', loc: [0, 0]}),
+                iD.Node({id: 'b', loc: [1, 1]}),
+                iD.Node({id: 'c', loc: [2, 0]}),
+                iD.Node({id: 'd', loc: [3, 0]}),
+                iD.Way({id: '-', nodes: ['a', 'b', 'c', 'd']})
+            ]);
+
+            expect(iD.actions.Straighten('-', projection).disabled(graph)).to.equal('too_bendy');
+        });
+
+        it("returns 'too_bendy' for ways with coincident start/end nodes", function () {
+            var graph = iD.Graph([
+                iD.Node({id: 'a', loc: [0, 0]}),
+                iD.Node({id: 'b', loc: [1, 0]}),
+                iD.Node({id: 'c', loc: [2, 0]}),
+                iD.Node({id: 'd', loc: [0, 0]}),
+                iD.Way({id: '-', nodes: ['a', 'b', 'c', 'd']})
+            ]);
+
+            expect(iD.actions.Straighten('-', projection).disabled(graph)).to.equal('too_bendy');
+        });
+    });
+
     it("deletes empty nodes", function() {
         var graph = iD.Graph([
                 iD.Node({id: 'a', loc: [0, 0]}),
@@ -10,7 +48,7 @@ describe("iD.actions.Straighten", function () {
             ]);
 
         graph = iD.actions.Straighten('-', projection)(graph);
-        
+
         expect(graph.hasEntity('b')).to.eq(undefined);
     });
 
@@ -23,10 +61,10 @@ describe("iD.actions.Straighten", function () {
             ]);
 
         graph = iD.actions.Straighten('-', projection)(graph);
-        
+
         expect(graph.entity('-').nodes).to.eql(['a', 'b', 'c']);
     });
-    
+
     it("does not delete nodes connected to other ways", function() {
         var graph = iD.Graph([
                 iD.Node({id: 'a', loc: [0, 0]}),
@@ -38,7 +76,7 @@ describe("iD.actions.Straighten", function () {
             ]);
 
         graph = iD.actions.Straighten('-', projection)(graph);
-        
+
         expect(graph.entity('-').nodes).to.have.length(3);
     });
 });