diff --git a/rtdata/languages/default b/rtdata/languages/default
index a0eccd167..6589c3a43 100644
--- a/rtdata/languages/default
+++ b/rtdata/languages/default
@@ -1869,6 +1869,7 @@ TP_PERSPECTIVE_CAMERA_SHIFT_HORIZONTAL;Horizontal shift
 TP_PERSPECTIVE_CAMERA_SHIFT_VERTICAL;Vertical shift
 TP_PERSPECTIVE_CAMERA_YAW;Horizontal
 TP_PERSPECTIVE_CONTROL_LINES;Control lines
+TP_PERSPECTIVE_CONTROL_LINES_TOOLTIP;Correct perspective distortion by drawing control lines.\n\nTo draw a line, activate either the vertical or horizontal drawing button. Hold down the control key and click-and-drag to draw a line. At least two vertical lines are required for vertical perspective correction. The same is true for horizontal correction. Click the tick mark button to apply perspective correction.
 TP_PERSPECTIVE_HORIZONTAL;Horizontal
 TP_PERSPECTIVE_LABEL;Perspective
 TP_PERSPECTIVE_METHOD;Method
diff --git a/rtgui/perspective.cc b/rtgui/perspective.cc
index 00d6cfa49..d84e1747e 100644
--- a/rtgui/perspective.cc
+++ b/rtgui/perspective.cc
@@ -136,6 +136,7 @@ PerspCorrection::PerspCorrection () : FoldableToolPanel(this, "perspective", M("
     img_ctrl_lines_edit = ipers_draw;
 
     Gtk::HBox* control_lines_box = Gtk::manage (new Gtk::HBox());
+    control_lines_box->set_tooltip_text( M("TP_PERSPECTIVE_CONTROL_LINES_TOOLTIP") );
     Gtk::Label* control_lines_label = Gtk::manage (new Gtk::Label (M("TP_PERSPECTIVE_CONTROL_LINES") + ": "));
     control_lines_box->pack_start(*control_lines_label, Gtk::PACK_SHRINK);
     control_lines_box->pack_start(*lines_button_v);