diff --git a/src/geom/CoordinateSequence.cpp b/src/geom/CoordinateSequence.cpp
index a0ff679449..00d8a95da3 100644
--- a/src/geom/CoordinateSequence.cpp
+++ b/src/geom/CoordinateSequence.cpp
@@ -174,6 +174,22 @@ CoordinateSequence::add(const CoordinateSequence& cs)
     add(cs, 0, cs.size() - 1);
 }
 
+void
+CoordinateSequence::add(const CoordinateSequence& cs, std::size_t from, std::size_t to, bool allowRepeated)
+{
+    if (allowRepeated) {
+        add(cs, from, to);
+        return;
+    }
+    for (size_t i = from; i <= to; i++) {
+        if (size() == 0 || ! cs.getAt<CoordinateXY>(i).equals2D( back<CoordinateXY>())) {
+            add(cs, i, i);
+        }
+    }
+}
+
+/*
+//-- this code has a bug in it (fails to add last coordinate in some cases)
 void
 CoordinateSequence::add(const CoordinateSequence& cs, std::size_t from, std::size_t to, bool allowRepeated)
 {
@@ -217,6 +233,7 @@ CoordinateSequence::add(const CoordinateSequence& cs, std::size_t from, std::siz
         add(cs, first, to);
     }
 }
+//*/
 
 void
 CoordinateSequence::add(const CoordinateSequence& cs, bool allowRepeated) {
diff --git a/src/noding/SegmentNodeList.cpp b/src/noding/SegmentNodeList.cpp
index 962f4a7c30..a68c206186 100644
--- a/src/noding/SegmentNodeList.cpp
+++ b/src/noding/SegmentNodeList.cpp
@@ -37,6 +37,7 @@
 #if GEOS_DEBUG
 #include <iostream>
 #endif
+#include <iomanip>
 
 //
 using namespace geos::geom;
@@ -312,8 +313,11 @@ SegmentNodeList::getSplitCoordinates()
 void
 SegmentNodeList::addEdgeCoordinates(const SegmentNode* ei0, const SegmentNode* ei1, CoordinateSequence& coordList) const {
     auto pts = createSplitEdgePts(ei0, ei1);
+//std::cout << std::endl << std::setprecision(16) << "addEdgeCoordinates: " << *pts << std::endl;
     // Append pts to coordList
     coordList.add(*pts, false);
+//std::cout << "updated coord list: " << std::setprecision(16) << coordList << std::endl;
+
 }
 
 
diff --git a/tests/unit/operation/overlayng/PrecisionReducerTest.cpp b/tests/unit/operation/overlayng/PrecisionReducerTest.cpp
index 3b3f4f7ebb..7d9dc6ea0c 100644
--- a/tests/unit/operation/overlayng/PrecisionReducerTest.cpp
+++ b/tests/unit/operation/overlayng/PrecisionReducerTest.cpp
@@ -27,11 +27,11 @@ struct test_precisionreducer_data {
     WKTWriter w;
 
     void
-    checkReduce(const std::string& wkt, double gridSize, const std::string& wkt_expected)
+    checkReduce(const std::string& wkt, double scale, const std::string& wkt_expected)
     {
         std::unique_ptr<Geometry> geom = r.read(wkt);
         std::unique_ptr<Geometry> expected = r.read(wkt_expected);
-        PrecisionModel pm(1.0/gridSize);
+        PrecisionModel pm(scale);
         std::unique_ptr<Geometry> result = PrecisionReducer::reducePrecision(geom.get(), &pm);
         ensure_equals_geometry(result.get(), expected.get());
     }
@@ -142,7 +142,7 @@ template<>
 void object::test<11> ()
 {
     checkReduce("LINESTRING(-3 6, 9 1)",
-        2, "LINESTRING (-2 6, 10 2)");
+        0.5, "LINESTRING (-2 6, 10 2)");
 }
 
 // testCollapsedLine
@@ -170,9 +170,18 @@ void object::test<14> ()
 {
     checkReduce("POLYGON ((2 1, 3 1, 3 2, 2 1))",
     // checkReduce("POLYGON ((0 0, 4 0, 4 4, 0 4, 0 0), (1 1, 1 2, 2 1, 1 1), (1 2, 1 3, 2 3, 1 2), (2 3, 3 3, 3 2, 2 3))",
-        1.0/10, "POLYGON ((2 1, 3 1, 3 2, 2 1))");
+        10, "POLYGON ((2 1, 3 1, 3 2, 2 1))");
 }
 
+// see https://github.com/libgeos/geos/issues/811
+template<>
+template<>
+void object::test<15> ()
+{
+    checkReduce("POLYGON ((127.117461568 34.562519572, 127.117483252 34.5624884690001, 127.117603304 34.562319127, 127.117607152 34.562312309, 127.117607012 34.562312359, 127.117254733 34.5621607510001, 127.117746661 34.5620659730001, 127.117603496 34.5623196400001, 127.117484065 34.562488982, 127.117462315 34.562520066, 127.117245225 34.562385186, 127.117461568 34.562519572))",
+        100000, 
+        "POLYGON ((127.11775 34.56207, 127.11725 34.56216, 127.11761 34.56231, 127.11775 34.56207))");
+}
 
 
 } // namespace tut