diff --git a/gnu/packages/tcl.scm b/gnu/packages/tcl.scm
index 2d9bf1e592..f9a23c3230 100644
--- a/gnu/packages/tcl.scm
+++ b/gnu/packages/tcl.scm
@@ -135,14 +135,14 @@ (define-public expect
 (define-public tk
   (package
     (name "tk")
-    (version "8.6.4")
+    (version "8.6.6")
     (source (origin
              (method url-fetch)
              (uri (string-append "mirror://sourceforge/tcl/Tcl/"
                                  version "/tk" version "-src.tar.gz"))
              (sha256
               (base32
-               "1h96vp15zl5xz0d4qp6wjyrchqmrmdm3q5k22wkw9jaxbvw9vy88"))
+               "17diivcfcwdhp4v5zi6j9nkxncccjqkivhp363c4wx5lf4d3fb6n"))
              (patches (search-patches "tk-find-library.patch"))))
     (build-system gnu-build-system)
     (arguments