diff --git a/Canvas.cpp b/Canvas.cpp
index aa6c881..c81a0f1 100644
--- a/Canvas.cpp
+++ b/Canvas.cpp
@@ -994,6 +994,14 @@ void Canvas::solve_for_canvas()
                     break;
                 }
             }
+
+            if (Circle * circle = CURVE_AS_CIRCLE(curve)) {
+                if (*circle->rad < EPS && after_constraint) {
+                    sys.undoSolution();
+                    flag = true;
+                    break;
+                }
+            }
         }
     }
     if (flag && after_constraint) {