diff --git a/dev-ml/labltk/files/labltk-8.06.12-c99.patch b/dev-ml/labltk/files/labltk-8.06.12-c99.patch
new file mode 100644
index 0000000000000..1761f478bd766
--- /dev/null
+++ b/dev-ml/labltk/files/labltk-8.06.12-c99.patch
@@ -0,0 +1,11 @@
+--- a/support/cltkVar.c	2024-06-04 20:18:35.940518270 +0200
++++ b/support/cltkVar.c	2024-06-04 20:18:49.456367424 +0200
+@@ -75,7 +75,7 @@
+         Tcl_Interp *interp, char *part1, char *part2, int flags));
+  */
+ static char * tracevar(ClientData clientdata, Tcl_Interp *interp,
+-                char *name1, char *name2, int flags)
++                const char *name1, const char *name2, int flags)
+      /* interp -> Interpreter containing variable. */
+      /* name1  -> Name of variable. */
+      /* name2  -> Second part of variable name. */
diff --git a/dev-ml/labltk/labltk-8.06.12-r2.ebuild b/dev-ml/labltk/labltk-8.06.12-r2.ebuild
index 8842a41bed315..974b1280538d7 100644
--- a/dev-ml/labltk/labltk-8.06.12-r2.ebuild
+++ b/dev-ml/labltk/labltk-8.06.12-r2.ebuild
@@ -1,4 +1,4 @@
-# Copyright 1999-2023 Gentoo Authors
+# Copyright 1999-2024 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
@@ -25,6 +25,7 @@ PATCHES=(
 	"${FILESDIR}"/${PN}-8.06.9-configure-clang16.patch
 	"${FILESDIR}"/${P}-shuffle.patch
 	"${FILESDIR}"/${P}-c2x.patch
+	"${FILESDIR}"/${P}-c99.patch
 )
 
 src_prepare() {