diff --git a/web/app/arc.js b/web/app/arc.js
index 30c60eb5..75d8da24 100644
--- a/web/app/arc.js
+++ b/web/app/arc.js
@@ -53,9 +53,16 @@ TCAD.TWO.Arc.prototype.distanceB = function() {
 TCAD.TWO.Arc.prototype.drawImpl = function(ctx, scale) {
   ctx.beginPath();
   var r = this.radiusForDrawing();
-  ctx.arc(this.c.x, this.c.y, r,
-    Math.atan2(this.a.y - this.c.y, this.a.x - this.c.x),
-    Math.atan2(this.b.y - this.c.y, this.b.x - this.c.x));
+  var startAngle = Math.atan2(this.a.y - this.c.y, this.a.x - this.c.x);
+  var endAngle;
+  if ( this.a.isCoincidentTo(this.b) || 
+      (TCAD.utils.areEqual(this.a.x, this.b.x, TCAD.utils.TOLERANCE) && 
+       TCAD.utils.areEqual(this.a.y, this.b.y, TCAD.utils.TOLERANCE))) {
+    endAngle = startAngle + 2 * Math.PI;
+  } else {
+    endAngle = Math.atan2(this.b.y - this.c.y, this.b.x - this.c.x);
+  } 
+  ctx.arc(this.c.x, this.c.y, r, startAngle, endAngle);
   ctx.stroke();
 };
 
diff --git a/web/app/canvas.js b/web/app/canvas.js
index 074ffd8a..72061097 100644
--- a/web/app/canvas.js
+++ b/web/app/canvas.js
@@ -274,6 +274,15 @@ TCAD.TWO.SketchObject = function() {
   this.linked = [];
 };
 
+TCAD.TWO.SketchObject.prototype.isCoincidentTo = function(other) {
+  for (var i = 0; i < this.linked.length; i++) {
+    var obj = this.linked[i];
+    if (obj.id === other.id) {
+      return true;        
+    }
+  }
+  return false;
+};
 
 TCAD.TWO.SketchObject.prototype._translate = function(dx, dy, translated) {
   translated[this.id] = 'x';