diff --git a/pkgs/development/interpreters/tcl/8.5.nix b/pkgs/development/interpreters/tcl/8.5.nix
index 193ff4f9376..9daf67fe2bd 100644
--- a/pkgs/development/interpreters/tcl/8.5.nix
+++ b/pkgs/development/interpreters/tcl/8.5.nix
@@ -4,6 +4,8 @@ callPackage ./generic.nix (args // rec {
   release = "8.5";
   version = "${release}.18";
 
+  # Note: when updating, the hash in pkgs/development/libraries/tk/8.5.nix must also be updated!
+
   src = fetchurl {
     url = "mirror://sourceforge/tcl/tcl${version}-src.tar.gz";
     sha256 = "1jfkqp2fr0xh6xvaqx134hkfa5kh7agaqbxm6lhjbpvvc1xfaaq3";
diff --git a/pkgs/development/interpreters/tcl/8.6.nix b/pkgs/development/interpreters/tcl/8.6.nix
index 37a7fee8a85..03fcb831779 100644
--- a/pkgs/development/interpreters/tcl/8.6.nix
+++ b/pkgs/development/interpreters/tcl/8.6.nix
@@ -4,6 +4,8 @@ callPackage ./generic.nix (args // rec {
   release = "8.6";
   version = "${release}.11";
 
+  # Note: when updating, the hash in pkgs/development/libraries/tk/8.6.nix must also be updated!
+
   src = fetchurl {
     url = "mirror://sourceforge/tcl/tcl${version}-src.tar.gz";
     sha256 = "0n4211j80mxr6ql0xx52rig8r885rcbminfpjdb2qrw6hmk8c14c";
diff --git a/pkgs/development/libraries/tk/8.6.nix b/pkgs/development/libraries/tk/8.6.nix
index fdffbeba2c9..33e3f8e4167 100644
--- a/pkgs/development/libraries/tk/8.6.nix
+++ b/pkgs/development/libraries/tk/8.6.nix
@@ -4,7 +4,7 @@ callPackage ./generic.nix (args // {
 
   src = fetchurl {
     url = "mirror://sourceforge/tcl/tk${tcl.version}.1-src.tar.gz"; # TODO: remove '.1' for v8.6.10 or v8.7.x
-    sha256 = "1d7bfkxpacy33w5nahf73lkwxqpff44w1jplg7i2gmwgiaawvjwg";
+    sha256 = "1gh9k7l76qg9l0sb78ijw9xz4xl1af47aqbdifb6mjpf3cbsnv00";
   };
 
   patches = [ ./different-prefix-with-tcl.patch ] ++ lib.optionals stdenv.isDarwin [ ./Fix-bad-install_name-for-libtk8.6.dylib.patch ];