diff --git a/include/sdf/Plane.hh b/include/sdf/Plane.hh
index 3ba3d1b6e..c920a3801 100644
--- a/include/sdf/Plane.hh
+++ b/include/sdf/Plane.hh
@@ -52,7 +52,7 @@ namespace sdf
     /// \return The plane normal vector.
     public: ignition::math::Vector3d Normal() const;
 
-    /// \brief Set the plane normal vector. The _normal vector will be
+    /// \brief Set the plane normal vector. The normal vector will be
     /// normalized. See ignition::math::Vector3d Normal() for more information
     /// about the normal vector, such as the frame in which it is specified.
     /// \param[in] _normal The plane normal vector.
diff --git a/python/src/sdf/pyPlane.cc b/python/src/sdf/pyPlane.cc
index ac624528e..ac3fef7c4 100644
--- a/python/src/sdf/pyPlane.cc
+++ b/python/src/sdf/pyPlane.cc
@@ -42,7 +42,7 @@ void definePlane(pybind11::object module)
           "for a Visual or Collision object, then the normal is specified in "
           "the Visual or Collision frame, respectively.")
     .def("set_normal", &sdf::Plane::SetNormal,
-          "Set the plane normal vector. The _normal vector will be "
+          "Set the plane normal vector. The normal vector will be "
           "normalized. See ignition::math::Vector3d Normal() for more "
           "information about the normal vector, such as the frame in which it "
           "is specified.")