diff --git a/src/window.c b/src/window.c
index 254942d3ba4..1069e71da54 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2975,7 +2975,8 @@ DEFUN ("scroll-up", Fscroll_up, Sscroll_up, 0, 1, "P",
   "Scroll text of current window upward ARG lines; or near full screen if no ARG.\n\
 A near full screen is `next-screen-context-lines' less than a full screen.\n\
 Negative ARG means scroll downward.\n\
-When calling from a program, supply a number as argument or nil.")
+If ARG is the atom `-', scroll downward by nearly full screen.
+When calling from a program, supply as argument a number, nil, or '-.")
   (arg)
      Lisp_Object arg;
 {
@@ -2984,10 +2985,11 @@ When calling from a program, supply a number as argument or nil.")
 }
 
 DEFUN ("scroll-down", Fscroll_down, Sscroll_down, 0, 1, "P",
-  "Scroll text of current window downward ARG lines; or near full screen if no ARG.\n\
+  "Scroll text of current window down ARG lines; or near full screen if no ARG.\n\
 A near full screen is `next-screen-context-lines' less than a full screen.\n\
 Negative ARG means scroll upward.\n\
-When calling from a program, supply a number as argument or nil.")
+If ARG is the atom `-', scroll upward by nearly full screen.
+When calling from a program, supply as argument a number, nil, or '-.")
   (arg)
      Lisp_Object arg;
 {
@@ -3040,9 +3042,11 @@ showing that buffer is used.")
 
 DEFUN ("scroll-other-window", Fscroll_other_window, Sscroll_other_window, 0, 1, "P",
   "Scroll next window upward ARG lines; or near full screen if no ARG.\n\
+A near full screen is `next-screen-context-lines' less than a full screen.
 The next window is the one below the current one; or the one at the top\n\
 if the current one is at the bottom.  Negative ARG means scroll downward.\n\
-When calling from a program, supply a number as argument or nil.\n\
+If ARG is the atom `-', scroll downward by nearly full screen.
+When calling from a program, supply as argument a number, nil, or '-.\n\
 \n\
 If in the minibuffer, `minibuffer-scroll-window' if non-nil\n\
 specifies the window to scroll.\n\