diff --git a/pkgs/development/interpreters/ruby/ruby-1.9.3.nix b/pkgs/development/interpreters/ruby/ruby-1.9.3.nix
index e361824bb532..77880870dd95 100644
--- a/pkgs/development/interpreters/ruby/ruby-1.9.3.nix
+++ b/pkgs/development/interpreters/ruby/ruby-1.9.3.nix
@@ -48,6 +48,12 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  # Fix a build failure on systems with nix store optimisation.
+  # (The build process attempted to copy file a overwriting file b, where a and
+  # b are hard-linked, which results in cp returning a non-zero exit code.)
+  # https://github.com/NixOS/nixpkgs/issues/4266
+  postUnpack = ''rm "$sourceRoot/enc/unicode/name2ctype.h"'';
+
   patches = [
     ./ruby19-parallel-install.patch
     ./bitperfect-rdoc.patch
diff --git a/pkgs/development/interpreters/ruby/ruby-2.0.0.nix b/pkgs/development/interpreters/ruby/ruby-2.0.0.nix
index 22b13717cfcb..4b1240ebf751 100644
--- a/pkgs/development/interpreters/ruby/ruby-2.0.0.nix
+++ b/pkgs/development/interpreters/ruby/ruby-2.0.0.nix
@@ -48,6 +48,12 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  # Fix a build failure on systems with nix store optimisation.
+  # (The build process attempted to copy file a overwriting file b, where a and
+  # b are hard-linked, which results in cp returning a non-zero exit code.)
+  # https://github.com/NixOS/nixpkgs/issues/4266
+  postUnpack = ''rm "$sourceRoot/enc/unicode/name2ctype.h"'';
+
   patches = ops useRailsExpress [
     "${patchSet}/patches/ruby/2.0.0/p481/01-zero-broken-tests.patch"
     "${patchSet}/patches/ruby/2.0.0/p481/02-railsexpress-gc.patch"
diff --git a/pkgs/development/interpreters/ruby/ruby-2.1.0.nix b/pkgs/development/interpreters/ruby/ruby-2.1.0.nix
index fd0c278133bc..91c21016b242 100644
--- a/pkgs/development/interpreters/ruby/ruby-2.1.0.nix
+++ b/pkgs/development/interpreters/ruby/ruby-2.1.0.nix
@@ -49,6 +49,12 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  # Fix a build failure on systems with nix store optimisation.
+  # (The build process attempted to copy file a overwriting file b, where a and
+  # b are hard-linked, which results in cp returning a non-zero exit code.)
+  # https://github.com/NixOS/nixpkgs/issues/4266
+  postUnpack = ''rm "$sourceRoot/enc/unicode/name2ctype.h"'';
+
   patches = ops useRailsExpress [
     "${patchSet}/patches/ruby/2.1.0/railsexpress/01-current-2.1.1-fixes.patch"
     "${patchSet}/patches/ruby/2.1.0/railsexpress/02-zero-broken-tests.patch"
diff --git a/pkgs/development/interpreters/ruby/ruby-2.1.1.nix b/pkgs/development/interpreters/ruby/ruby-2.1.1.nix
index c60a6cb313d4..e70678e27ecc 100644
--- a/pkgs/development/interpreters/ruby/ruby-2.1.1.nix
+++ b/pkgs/development/interpreters/ruby/ruby-2.1.1.nix
@@ -49,6 +49,12 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  # Fix a build failure on systems with nix store optimisation.
+  # (The build process attempted to copy file a overwriting file b, where a and
+  # b are hard-linked, which results in cp returning a non-zero exit code.)
+  # https://github.com/NixOS/nixpkgs/issues/4266
+  postUnpack = ''rm "$sourceRoot/enc/unicode/name2ctype.h"'';
+
   patches = ops useRailsExpress [
     "${patchSet}/patches/ruby/2.1.0/railsexpress/01-zero-broken-tests.patch"
     "${patchSet}/patches/ruby/2.1.0/railsexpress/02-improve-gc-stats.patch"
diff --git a/pkgs/development/interpreters/ruby/ruby-2.1.2.nix b/pkgs/development/interpreters/ruby/ruby-2.1.2.nix
index 1738606bf140..929a14f8242b 100644
--- a/pkgs/development/interpreters/ruby/ruby-2.1.2.nix
+++ b/pkgs/development/interpreters/ruby/ruby-2.1.2.nix
@@ -49,6 +49,12 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  # Fix a build failure on systems with nix store optimisation.
+  # (The build process attempted to copy file a overwriting file b, where a and
+  # b are hard-linked, which results in cp returning a non-zero exit code.)
+  # https://github.com/NixOS/nixpkgs/issues/4266
+  postUnpack = ''rm "$sourceRoot/enc/unicode/name2ctype.h"'';
+
   patches = ops useRailsExpress [
     "${patchSet}/patches/ruby/2.1.2/railsexpress/01-zero-broken-tests.patch"
     "${patchSet}/patches/ruby/2.1.2/railsexpress/02-improve-gc-stats.patch"