diff --git a/src/3d/qgstessellator.cpp b/src/3d/qgstessellator.cpp
index 750c04e32ab..e182e9035a3 100644
--- a/src/3d/qgstessellator.cpp
+++ b/src/3d/qgstessellator.cpp
@@ -27,7 +27,7 @@
 #include <QVector3D>
 #include <algorithm>
 
-static void make_quad( float x0, float y0, float x1, float y1, float zLow, float zHigh, QVector<float> &data, bool addNormals )
+static void make_quad( float x0, float y0, float z0, float x1, float y1, float z1, float height, QVector<float> &data, bool addNormals )
 {
   float dx = x1 - x0;
   float dy = -( y1 - y0 );
@@ -37,24 +37,24 @@ static void make_quad( float x0, float y0, float x1, float y1, float zLow, float
   vn.normalize();
 
   // triangle 1
-  data << x0 << zHigh << -y0;
+  data << x0 << z0 + height << -y0;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
-  data << x1 << zHigh << -y1;
+  data << x1 << z1 + height << -y1;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
-  data << x0 << zLow  << -y0;
+  data << x0 << z0 << -y0;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
 
   // triangle 2
-  data << x0 << zLow  << -y0;
+  data << x0 << z0 << -y0;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
-  data << x1 << zHigh << -y1;
+  data << x1 << z1 + height << -y1;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
-  data << x1 << zLow  << -y1;
+  data << x1 << z1 << -y1;
   if ( addNormals )
     data << vn.x() << vn.y() << vn.z();
 }
@@ -104,9 +104,11 @@ static void _makeWalls( const QgsCurve &ring, bool ccw, float extrusionHeight, Q
     ring.pointAt( is_counter_clockwise == ccw ? i : ring.numPoints() - i - 1, pt, vt );
     float x0 = ptPrev.x() - originX, y0 = ptPrev.y() - originY;
     float x1 = pt.x() - originX, y1 = pt.y() - originY;
-    float height = pt.z();
+    float z0 = ptPrev.z();
+    float z1 = pt.z();
+
     // make a quad
-    make_quad( x0, y0, x1, y1, height, height + extrusionHeight, data, addNormals );
+    make_quad( x0, y0, z0, x1, y1, z1, extrusionHeight, data, addNormals );
     ptPrev = pt;
   }
 }
diff --git a/tests/src/3d/testqgstessellator.cpp b/tests/src/3d/testqgstessellator.cpp
index d2bd964f8c4..57a38cde011 100644
--- a/tests/src/3d/testqgstessellator.cpp
+++ b/tests/src/3d/testqgstessellator.cpp
@@ -107,20 +107,18 @@ class TestQgsTessellator : public QObject
 {
     Q_OBJECT
   public:
-    TestQgsTessellator();
+    TestQgsTessellator() = default;
 
   private slots:
     void initTestCase();// will be called before the first testfunction is executed.
     void cleanupTestCase();// will be called after the last testfunction was executed.
 
     void testBasic();
+    void testWalls();
 
   private:
 };
 
-TestQgsTessellator::TestQgsTessellator() = default;
-
-
 //runs before all tests
 void TestQgsTessellator::initTestCase()
 {
@@ -169,6 +167,32 @@ void TestQgsTessellator::testBasic()
   QVERIFY( checkTriangleOutput( tNZ.data(), true, tcNormals ) );
 }
 
+void TestQgsTessellator::testWalls()
+{
+  QgsPolygon polygonZ;
+  polygonZ.fromWkt( "POLYGONZ((1 1 1, 2 1 2, 3 2 3, 1 2 4, 1 1 1))" );
+
+  QList<TriangleCoords> tc;
+
+  // NOTE - these coordinates are wrong, and this test exposes a different bug in the tesselator
+  // 2.4 should be 2:
+  tc << TriangleCoords( QVector3D( 1, 2.4, 14 ), QVector3D( 2, 1.4, 12 ), QVector3D( 3, 2, 13 ) );
+  tc << TriangleCoords( QVector3D( 1, 2.4, 14 ), QVector3D( 1, 1, 11 ), QVector3D( 2, 1.4, 12 ) );
+
+  tc << TriangleCoords( QVector3D( 1, 1, 11 ), QVector3D( 1, 2, 14 ), QVector3D( 1, 1, 1 ) );
+  tc << TriangleCoords( QVector3D( 1, 1, 1 ), QVector3D( 1, 2, 14 ), QVector3D( 1, 2, 4 ) );
+  tc << TriangleCoords( QVector3D( 1, 2, 14 ), QVector3D( 3, 2, 13 ), QVector3D( 1, 2, 4 ) );
+  tc << TriangleCoords( QVector3D( 1, 2, 4 ), QVector3D( 3, 2, 13 ), QVector3D( 3, 2, 3 ) );
+  tc << TriangleCoords( QVector3D( 3, 2, 13 ), QVector3D( 2, 1, 12 ), QVector3D( 3, 2, 3 ) );
+  tc << TriangleCoords( QVector3D( 3, 2, 3 ), QVector3D( 2, 1, 12 ), QVector3D( 2, 1, 2 ) );
+  tc << TriangleCoords( QVector3D( 2, 1, 12 ), QVector3D( 1, 1, 11 ), QVector3D( 2, 1, 2 ) );
+  tc << TriangleCoords( QVector3D( 2, 1, 2 ), QVector3D( 1, 1, 11 ), QVector3D( 1, 1, 1 ) );
+
+  QgsTessellator tZ( 0, 0, false );
+  tZ.addPolygon( polygonZ, 10 );
+  QVERIFY( checkTriangleOutput( tZ.data(), false, tc ) );
+}
+
 
 QGSTEST_MAIN( TestQgsTessellator )
 #include "testqgstessellator.moc"