diff --git a/gntwm.h b/gntwm.h
--- a/gntwm.h
+++ b/gntwm.h
@@ -51,9 +51,7 @@
  *
  * A node in the window management tree.
  */
-typedef struct _GntNode GntNode;
-
-struct _GntNode
+typedef struct
 {
        GntWidget *me;

@@ -61,7 +59,7 @@ struct _GntNode
        int scroll;
        PANEL *panel;
        GntWS *ws;
-};
+} GntNode;

 G_BEGIN_DECLS


Gives us the same warning of

[1/1] Generating libgnt-doc with a custom command
Building documentation for libgnt
html/libgnt-gntwm.html:643: warning: no link for: "GntNode" -> (<span class="type">GntNode</span>).

Odd, it seemed to have worked for me:
$ hg di
diff --git a/gntwm.h b/gntwm.h
--- a/gntwm.h
+++ b/gntwm.h
@@ -51,8 +51,7 @@
  *
  * A node in the window management tree.
  */
-typedef struct _GntNode
-{
+typedef struct {
        GntWidget *me;

        WINDOW *window;

$ ninja -C build clean
ninja: Entering directory `build'
[2/2] Cleaning
Cleaning... 28 files.

$ ninja -C build libgnt-doc
ninja: Entering directory `build'
[9/28] Compiling C object libgnt.so.1.0.0.p/gntmain.c.o
... warning stuff ...
[28/28] Generating libgnt-doc with a custom command
Building documentation for libgnt
html/api-index-full.html:1140: warning: no link for: "gnt-text-format-flag-to-chtype" -> (gnt_text_format_flag_to_chtype).
html/api-index-full.html:1140: warning: no link for: "libgnt-gnttextviewprivate" -> (gnttextviewprivate).
html/libgnt-gntwm.html:994: warning: no link for: "WINDOW:CAPS" -> (<span class="type">WINDOW</span>).
html/libgnt-gntwm.html:1004: warning: no link for: "PANEL:CAPS" -> (<span class="type">PANEL</span>).