diff --git a/src/constraint.cpp b/src/constraint.cpp
index 93831731..435fc3ac 100644
--- a/src/constraint.cpp
+++ b/src/constraint.cpp
@@ -127,7 +127,7 @@ hConstraint Constraint::ConstrainCoincident(hEntity ptA, hEntity ptB) {
         Entity::NO_ENTITY, Entity::NO_ENTITY, /*other=*/false, /*other2=*/false);
 }
 
-void Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc) {
+bool Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc) {
     Vector l0 = SK.GetEntity(line->point[0])->PointGetNum(),
            l1 = SK.GetEntity(line->point[1])->PointGetNum();
     Vector a1 = SK.GetEntity(arc->point[1])->PointGetNum(),
@@ -140,11 +140,12 @@ void Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *ar
         Error(_("The tangent arc and line segment must share an "
                 "endpoint. Constrain them with Constrain -> "
                 "On Point before constraining tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
-void Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic) {
+bool Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic) {
     Vector l0 = SK.GetEntity(line->point[0])->PointGetNum(),
            l1 = SK.GetEntity(line->point[1])->PointGetNum();
     Vector as = cubic->CubicGetStartNum(),
@@ -158,11 +159,12 @@ void Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *
         Error(_("The tangent cubic and line segment must share an "
                 "endpoint. Constrain them with Constrain -> "
                 "On Point before constraining tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
-void Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB) {
+bool Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB) {
     Vector as = eA->EndpointStart(),
            af = eA->EndpointFinish(),
            bs = eB->EndpointStart(),
@@ -183,8 +185,9 @@ void Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *e
         Error(_("The curves must share an endpoint. Constrain them "
                 "with Constrain -> On Point before constraining "
                 "tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
 void Constraint::MenuConstrain(Command id) {
@@ -690,7 +693,9 @@ void Constraint::MenuConstrain(Command id) {
                 if(line->type == Entity::Type::ARC_OF_CIRCLE) {
                     swap(line, arc);
                 }
-                ConstrainArcLineTangent(&c, line, arc);
+                if(!ConstrainArcLineTangent(&c, line, arc)) {
+                    return;
+                }
                 c.type = Type::ARC_LINE_TANGENT;
                 c.entityA = arc->h;
                 c.entityB = line->h;
@@ -700,7 +705,9 @@ void Constraint::MenuConstrain(Command id) {
                 if(line->type == Entity::Type::CUBIC) {
                     swap(line, cubic);
                 }
-                ConstrainCubicLineTangent(&c, line, cubic);
+                if(!ConstrainCubicLineTangent(&c, line, cubic)) {
+                    return;
+                }
                 c.type = Type::CUBIC_LINE_TANGENT;
                 c.entityA = cubic->h;
                 c.entityB = line->h;
@@ -711,7 +718,9 @@ void Constraint::MenuConstrain(Command id) {
                 }
                 Entity *eA = SK.GetEntity(gs.entity[0]),
                        *eB = SK.GetEntity(gs.entity[1]);
-                ConstrainCurveCurveTangent(&c, eA, eB);
+                if(!ConstrainCurveCurveTangent(&c, eA, eB)) {
+                    return;
+                }
                 c.type = Type::CURVE_CURVE_TANGENT;
                 c.entityA = eA->h;
                 c.entityB = eB->h;
diff --git a/src/sketch.h b/src/sketch.h
index 83773749..903e638f 100644
--- a/src/sketch.h
+++ b/src/sketch.h
@@ -790,9 +790,9 @@ public:
     static hConstraint TryConstrain(Constraint::Type type, hEntity ptA, hEntity ptB,
                                     hEntity entityA, hEntity entityB = Entity::NO_ENTITY,
                                     bool other = false, bool other2 = false);
-    static void ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc);
-    static void ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic);
-    static void ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB);
+    static bool ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc);
+    static bool ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic);
+    static bool ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB);
 };
 
 class hEquation {