diff --git a/pkgs/applications/misc/wordnet/default.nix b/pkgs/applications/misc/wordnet/default.nix
index f63d61b0ea48..86213a8b3d66 100644
--- a/pkgs/applications/misc/wordnet/default.nix
+++ b/pkgs/applications/misc/wordnet/default.nix
@@ -15,7 +15,7 @@ stdenv.mkDerivation {
                    "--with-tk="  + tk  + "/lib";
 
   postInstall = ''
-    wrapProgram $out/bin/wishwn --set TK_LIBRARY "${tk}/lib/tk8.4"
+    wrapProgram $out/bin/wishwn --set TK_LIBRARY "${tk}/lib/${tk.libPrefix}"
     wrapProgram $out/bin/wnb    --prefix PATH : "$out/bin"
   '';
 
diff --git a/pkgs/applications/version-management/git-and-tools/git/default.nix b/pkgs/applications/version-management/git-and-tools/git/default.nix
index 9f7149d6663b..b7d34906c4a8 100644
--- a/pkgs/applications/version-management/git-and-tools/git/default.nix
+++ b/pkgs/applications/version-management/git-and-tools/git/default.nix
@@ -82,7 +82,7 @@ stdenv.mkDerivation rec {
        for prog in bin/gitk libexec/git-core/git-gui
        do
          wrapProgram "$out/$prog"                       \
-                     --set TK_LIBRARY "${tk}/lib/tk8.4" \
+                     --set TK_LIBRARY "${tk}/lib/${tk.libPrefix}" \
                      --prefix PATH : "${tk}/bin"
        done
      '' else ''
diff --git a/pkgs/applications/version-management/git-and-tools/git/git-git.nix b/pkgs/applications/version-management/git-and-tools/git/git-git.nix
index 0e4efa26fd32..a3b2a60953a5 100644
--- a/pkgs/applications/version-management/git-and-tools/git/git-git.nix
+++ b/pkgs/applications/version-management/git-and-tools/git/git-git.nix
@@ -72,7 +72,7 @@ stdenv.mkDerivation rec {
 
    + (if guiSupport then ''
        # Wrap Tcl/Tk programs
-         wrapArgs="$wrapArgs --set TK_LIBRARY ${tk}/lib/tk8.4"
+         wrapArgs="$wrapArgs --set TK_LIBRARY ${tk}/lib/${tk.libPrefix}"
          wrapArgs="$wrapArgs --prefix PATH : ${tk}/bin"
      '' else "")
 
diff --git a/pkgs/applications/version-management/mercurial/default.nix b/pkgs/applications/version-management/mercurial/default.nix
index 198d14395144..054dd0c1813a 100644
--- a/pkgs/applications/version-management/mercurial/default.nix
+++ b/pkgs/applications/version-management/mercurial/default.nix
@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
       hgk=$out/lib/${python.libPrefix}/site-packages/hgext/hgk.py
       EOF
       # setting HG so that hgk can be run itself as well (not only hg view)
-      WRAP_TK=" --set TK_LIBRARY \"${tk}/lib/tk8.4\"
+      WRAP_TK=" --set TK_LIBRARY \"${tk}/lib/${tk.libPrefix}\"
                 --set HG \"$out/bin/hg\"
                 --prefix PATH : \"${tk}/bin\" "
     ''
diff --git a/pkgs/development/libraries/tk/default.nix b/pkgs/development/libraries/tk/default.nix
index bf6da7b65982..290580e52129 100644
--- a/pkgs/development/libraries/tk/default.nix
+++ b/pkgs/development/libraries/tk/default.nix
@@ -19,4 +19,8 @@ stdenv.mkDerivation {
   buildInputs = [tcl x11];
   
   inherit tcl;
+
+  passthru = {
+    libPrefix = "tk8.5";
+  };
 }