diff --git a/SDL_ttf.h b/SDL_ttf.h
--- a/SDL_ttf.h
+++ b/SDL_ttf.h
@@ -247,8 +247,21 @@
 /* Check if the TTF engine is initialized */
 extern DECLSPEC int SDLCALL TTF_WasInit(void);
 
-/* Get the kerning size of two glyphs */
-extern DECLSPEC int TTF_GetFontKerningSize(TTF_Font *font, Uint16 previous_ch, Uint16 ch);
+/*  Get the kerning size of two glyphs.
+
+    kerning A pointer filled in with the kerning pair size.
+
+    This function returns zero (0) on success, or a negative error code on
+    failure; call TTF_GetError() for more information.
+
+    Kerning distances are expressed in pixels. They are usually oriented in the
+    X axis, which means that a negative value indicates that two glyphs must be
+    set closer in a horizontal layout.
+
+    See also: http://www.freetype.org/freetype2/docs/glyphs/glyphs-4.html
+*/
+extern DECLSPEC int TTF_GetFontKerningSize( TTF_Font *font, Uint16 previous_ch,
+                                            Uint16 ch, int* kerning );
 
 /* We'll use SDL for reporting errors */
 #define TTF_SetError    SDL_SetError