diff --git a/src/Mod/Sketcher/Gui/CommandConstraints.cpp b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
index 51e9b139a..4970e8cce 100644
--- a/src/Mod/Sketcher/Gui/CommandConstraints.cpp
+++ b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
@@ -23,7 +23,9 @@
 
 #include "PreCompiled.h"
 #ifndef _PreComp_
+# include <cfloat>
 # include <QMessageBox>
+# include <Precision.hxx>
 #endif
 
 #include <App/Application.h>
@@ -1562,8 +1564,8 @@ void CmdSketcherConstrainAngle::activated(int iMsg)
             Base::Vector3d p1b = lineSeg1->getEndPoint();
             Base::Vector3d p2a = lineSeg2->getStartPoint();
             Base::Vector3d p2b = lineSeg2->getEndPoint();
-            double length = 1e10;
-            for (int i=0; i <= 1; i++)
+            double length = DBL_MAX;
+            for (int i=0; i <= 1; i++) {
                 for (int j=0; j <= 1; j++) {
                     double tmp = ((j?p2a:p2b)-(i?p1a:p1b)).Length();
                     if (tmp < length) {
@@ -1572,12 +1574,24 @@ void CmdSketcherConstrainAngle::activated(int iMsg)
                         PosId2 = j ? Sketcher::start : Sketcher::end;
                     }
                 }
+            }
 
             Base::Vector3d dir1 = ((PosId1 == Sketcher::start) ? 1. : -1.) *
                                   (lineSeg1->getEndPoint()-lineSeg1->getStartPoint());
             Base::Vector3d dir2 = ((PosId2 == Sketcher::start) ? 1. : -1.) *
                                   (lineSeg2->getEndPoint()-lineSeg2->getStartPoint());
 
+            // check if the two lines are parallel, in this case an angle is not possible
+            Base::Vector3d dir3 = dir1 % dir2;
+            if (dir3.Length() < Precision::Intersection()) {
+                Base::Vector3d dist = (p1a - p2a) % dir1;
+                if (dist.Sqr() > Precision::Intersection()) {
+                    QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Parallel lines"),
+                        QObject::tr("An angle constraint cannot be set for two parallel lines."));
+                    return;
+                }
+            }
+
             double ActAngle = atan2(-dir1.y*dir2.x+dir1.x*dir2.y,
                                     dir1.x*dir2.x+dir1.y*dir2.y);
             if (ActAngle < 0) {
diff --git a/src/Mod/Sketcher/Gui/SoDatumLabel.cpp b/src/Mod/Sketcher/Gui/SoDatumLabel.cpp
index 7e9f90ccb..b0c38ebe3 100644
--- a/src/Mod/Sketcher/Gui/SoDatumLabel.cpp
+++ b/src/Mod/Sketcher/Gui/SoDatumLabel.cpp
@@ -441,7 +441,7 @@ void SoDatumLabel::GLRender(SoGLRenderAction * action)
 
     SbVec2s size;
     int nc;
-    int srcw, srch;
+    int srcw=1, srch=1;
 
     if (hasText) {
         if (!this->glimagevalid) {
diff --git a/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp b/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
index 5051b01f4..b51ef41be 100644
--- a/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
+++ b/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
@@ -2661,13 +2661,32 @@ Restart:
                         // line-line intersection
                         {
                             double det = dir1.x*dir2.y - dir1.y*dir2.x;
-                            if ((det > 0 ? det : -det) < 1e-10)
-                                break;
-                            double c1 = dir1.y*pnt1.x - dir1.x*pnt1.y;
-                            double c2 = dir2.y*pnt2.x - dir2.x*pnt2.y;
-                            double x = (dir1.x*c2 - dir2.x*c1)/det;
-                            double y = (dir1.y*c2 - dir2.y*c1)/det;
-                            p0 = SbVec3f(x,y,0);
+                            if ((det > 0 ? det : -det) < 1e-10) {
+                                // lines are coincident (or parallel) and in this case the center
+                                // of the point pairs with the shortest distance is used
+                                Base::Vector3d p1[2], p2[2];
+                                p1[0] = lineSeg1->getStartPoint();
+                                p1[1] = lineSeg1->getEndPoint();
+                                p2[0] = lineSeg2->getStartPoint();
+                                p2[1] = lineSeg2->getEndPoint();
+                                double length = DBL_MAX;
+                                for (int i=0; i <= 1; i++) {
+                                    for (int j=0; j <= 1; j++) {
+                                        double tmp = (p2[j]-p1[i]).Length();
+                                        if (tmp < length) {
+                                            length = tmp;
+                                            p0.setValue((p2[j].x+p1[i].x)/2,(p2[j].y+p1[i].y)/2,0);
+                                        }
+                                    }
+                                }
+                            }
+                            else {
+                                double c1 = dir1.y*pnt1.x - dir1.x*pnt1.y;
+                                double c2 = dir2.y*pnt2.x - dir2.x*pnt2.y;
+                                double x = (dir1.x*c2 - dir2.x*c1)/det;
+                                double y = (dir1.y*c2 - dir2.y*c1)/det;
+                                p0 = SbVec3f(x,y,0);
+                            }
                         }
 
                         startangle = atan2(dir1.y,dir1.x);