diff --git a/FL/Fl_Graphics_Driver.H b/FL/Fl_Graphics_Driver.H
index daa1232ca..0c98afdad 100644
--- a/FL/Fl_Graphics_Driver.H
+++ b/FL/Fl_Graphics_Driver.H
@@ -225,7 +225,7 @@ public:
   Fl_Graphics_Driver();
   virtual ~Fl_Graphics_Driver() {} ///< Destructor
   static Fl_Graphics_Driver &default_driver();
-  /** Current scale factor between FLTK and graphical coordinates: graphical = FLTK * scale() */
+  /** Current scale factor between FLTK and drawing units: drawing = FLTK * scale() */
   float scale() { return scale_; }
   /** Return whether the graphics driver can do alpha blending */
   virtual char can_do_alpha_blending() { return 0; }
diff --git a/documentation/src/drawing.dox b/documentation/src/drawing.dox
index c6e8e8843..178843f2c 100644
--- a/documentation/src/drawing.dox
+++ b/documentation/src/drawing.dox
@@ -1154,6 +1154,10 @@ void fl_copy_offscreen(int x, int y, int w, int h, Fl_Offscreen osrc, int srcx,
 Copy a rectangular area of the size \p w*h from \p srcx,srcy
 in the offscreen buffer into the current drawing surface at \p x,y.
 
+void fl_scale_offscreen(Fl_Offscreen &osrc)
+\par
+Adapts the offscreen's size in pixels to a changed value of the scale factor
+while keeping the offscreen's graphical content.
 
 \htmlonly
 <hr>
diff --git a/src/Fl_Image_Surface.cxx b/src/Fl_Image_Surface.cxx
index bf115dcfa..9333d858a 100644
--- a/src/Fl_Image_Surface.cxx
+++ b/src/Fl_Image_Surface.cxx
@@ -186,9 +186,12 @@ void fl_end_offscreen() {
   Fl_Surface_Device::pop_current();
 }
 
-/** Adapts an offscreen buffer to a changed value of the graphical scaling factor.
+/** Adapts an offscreen buffer to a changed value of the scale factor.
  The \p ctx argument must have been created by fl_create_offscreen()
  and the calling context must not be between fl_begin_offscreen() and fl_end_offscreen().
+ The graphical content of the offscreen is preserved. The current scale factor
+ value is given by <tt>Fl_Graphics_Driver::default_driver().scale()</tt>.
+ \version 1.4
  */
 void fl_scale_offscreen(Fl_Offscreen &ctx) {
   int i, w, h;