diff --git a/include/geos/operation/buffer/OffsetSegmentGenerator.h b/include/geos/operation/buffer/OffsetSegmentGenerator.h
index 2f3a369c69..75affa0f36 100644
--- a/include/geos/operation/buffer/OffsetSegmentGenerator.h
+++ b/include/geos/operation/buffer/OffsetSegmentGenerator.h
@@ -144,7 +144,8 @@ class GEOS_DLL OffsetSegmentGenerator {
     /// Add an end cap around point p1, terminating a line segment
     /// coming from p0
     void addLineEndCap(const geom::Coordinate& p0,
-                       const geom::Coordinate& p1);
+                       const geom::Coordinate& p1,
+                       const geom::Coordinate& p2);
 
     void
     addSegments(const geom::CoordinateSequence& pts, bool isForward)
diff --git a/src/operation/buffer/OffsetCurveBuilder.cpp b/src/operation/buffer/OffsetCurveBuilder.cpp
index 1628ef9bb2..1e0f0b1757 100644
--- a/src/operation/buffer/OffsetCurveBuilder.cpp
+++ b/src/operation/buffer/OffsetCurveBuilder.cpp
@@ -377,8 +377,6 @@ OffsetCurveBuilder::computeLineBufferCurve(const CoordinateSequence& inputPts,
         segGen.addNextSegment(simp1[i], true);
     }
     segGen.addLastSegment();
-    // add line cap for end of line
-    segGen.addLineEndCap(simp1[n1 - 1], simp1[n1]);
 
     //---------- compute points for right side of line
     // Simplify the appropriate side of the line before generating
@@ -387,13 +385,17 @@ OffsetCurveBuilder::computeLineBufferCurve(const CoordinateSequence& inputPts,
     const CoordinateSequence& simp2 = *simp2_;
 
     auto n2 = simp2.size() - 1;
+
+    // add line cap for return of line
+    segGen.addLineEndCap(simp1[n1 - 1], simp1[n1], simp2[n2 - 1]);
+
     segGen.initSideSegments(simp2[n2], simp2[n2 - 1], Position::LEFT);
     for(std::size_t i = n2 - 1; i > 0; --i) {
         segGen.addNextSegment(simp2[i - 1], true);
     }
     segGen.addLastSegment();
     // add line cap for start of line
-    segGen.addLineEndCap(simp2[1], simp2[0]);
+    segGen.addLineEndCap(simp2[1], simp2[0], simp1[1]);
 
     segGen.closeRing();
 }
diff --git a/src/operation/buffer/OffsetSegmentGenerator.cpp b/src/operation/buffer/OffsetSegmentGenerator.cpp
index 6c7c2c3b08..435d4770ad 100644
--- a/src/operation/buffer/OffsetSegmentGenerator.cpp
+++ b/src/operation/buffer/OffsetSegmentGenerator.cpp
@@ -187,25 +187,21 @@ OffsetSegmentGenerator::computeOffsetSegment(const LineSegment& seg, int p_side,
 
 /*public*/
 void
-OffsetSegmentGenerator::addLineEndCap(const Coordinate& p0, const Coordinate& p1)
+OffsetSegmentGenerator::addLineEndCap(const Coordinate& p0, const Coordinate& p1, const Coordinate& p2)
 {
-    LineSegment seg(p0, p1);
+    LineSegment segL(p0, p1);
+    LineSegment segR(p2, p1);
 
     LineSegment offsetL;
-    computeOffsetSegment(seg, Position::LEFT, distance, offsetL);
+    computeOffsetSegment(segL, Position::LEFT, distance, offsetL);
     LineSegment offsetR;
-    computeOffsetSegment(seg, Position::RIGHT, distance, offsetR);
-
-    double dx = p1.x - p0.x;
-    double dy = p1.y - p0.y;
-    double angle = atan2(dy, dx);
+    computeOffsetSegment(segR, Position::RIGHT, distance, offsetR);
 
     switch(bufParams.getEndCapStyle()) {
     case BufferParameters::CAP_ROUND:
         // add offset seg points with a fillet between them
         segList.addPt(offsetL.p1);
-        addDirectedFillet(p1, angle + Angle::PI_OVER_2, angle - Angle::PI_OVER_2,
-                  Orientation::CLOCKWISE, distance);
+        addDirectedFillet(p1, offsetL.p1, offsetR.p1, Orientation::CLOCKWISE, distance);
         segList.addPt(offsetR.p1);
         break;
     case BufferParameters::CAP_FLAT:
@@ -216,7 +212,12 @@ OffsetSegmentGenerator::addLineEndCap(const Coordinate& p0, const Coordinate& p1
     case BufferParameters::CAP_SQUARE:
         // add a square defined by extensions of the offset
         // segment endpoints
+
         Coordinate squareCapSideOffset;
+        // take average in case angles of left and right sides differ
+        double dx = p1.x - p0.x/2 - p2.x/2;
+        double dy = p1.y - p0.y/2 - p2.y/2;
+        double angle = atan2(dy, dx);
         double sinangle, cosangle;
         Angle::sinCosSnap(angle, sinangle, cosangle);
         squareCapSideOffset.x = fabs(distance) * cosangle;
diff --git a/tests/unit/operation/buffer/BufferOpTest.cpp b/tests/unit/operation/buffer/BufferOpTest.cpp
index b51914ca8d..1c5d3ceadb 100644
--- a/tests/unit/operation/buffer/BufferOpTest.cpp
+++ b/tests/unit/operation/buffer/BufferOpTest.cpp
@@ -623,4 +623,18 @@ void object::test<28>
 "MULTIPOLYGON (((24 95.239, 24 96, 24 99, 24.816 99, 24 95.239)), ((3 90, 3 93, 3 96, 3 99, 21 99, 21 96, 21 93, 21 90, 3 90)))");    
 }
 
+// testEndCap
+// test end cap for a line where left and right side are simplified differently, so there is an angle at the end
+// See https://github.com/libgeos/geos/issues/1217
+template<>
+template<>
+void object::test<29>
+()
+{
+    std::string wkt("LINESTRING (0.7 4.7, 146.3 137.1, 146.3 137, 146.6 136.7)");
+    std::unique_ptr<Geometry> result13 = buffer(wkt, 11);	
+    checkValidPolygon(*result13);
+    checkNumHoles(*result13, 0);
+}
+
 } // namespace tut