diff --git a/pkgs/development/interpreters/ruby/gem.nix b/pkgs/development/interpreters/ruby/gem.nix
index dd6338cd813d..bbc38226266b 100644
--- a/pkgs/development/interpreters/ruby/gem.nix
+++ b/pkgs/development/interpreters/ruby/gem.nix
@@ -6,7 +6,7 @@ lib.makeOverridable (
 , ruby ? defs.ruby
 , rubygems ? (rubygemsFun ruby)
 , stdenv ? ruby.stdenv
-, namePrefix ? "${ruby.name}" + "-"
+, namePrefix ? "${lib.replaceStrings ["-"] ["_"] ruby.name}" + "-"
 , buildInputs ? []
 , doCheck ? false
 , dontBuild ? true