diff --git a/raster/r.horizon/main.c b/raster/r.horizon/main.c
index ec6f0c4f50e..11bab7cf421 100644
--- a/raster/r.horizon/main.c
+++ b/raster/r.horizon/main.c
@@ -757,6 +757,7 @@ double horizon_height(void)
 
     tanh0 = 0.;
     length = 0;
+    zp = z_orig;
 
     height = searching();
 
diff --git a/raster/r.horizon/testsuite/test_r_horizon.py b/raster/r.horizon/testsuite/test_r_horizon.py
index 8111e5d9791..b43e7a2d3d9 100644
--- a/raster/r.horizon/testsuite/test_r_horizon.py
+++ b/raster/r.horizon/testsuite/test_r_horizon.py
@@ -144,6 +144,12 @@ def test_point_mode_multiple_direction(self):
         stdout = module.outputs.stdout
         self.assertMultiLineEqual(first=ref2, second=stdout)
 
+        # include nulls along the edge
+        self.runModule("g.region", raster="elevation", w="w-100")
+        self.assertModule(module)
+        stdout = module.outputs.stdout
+        self.assertMultiLineEqual(first=ref2, second=stdout)
+
     def test_point_mode_multiple_direction_artificial(self):
         """Test mode with 1 point and multiple directions with artificial surface"""
         module = SimpleModule(