diff --git a/pkgs/development/ruby-modules/gem-config/default.nix b/pkgs/development/ruby-modules/gem-config/default.nix
index 9f2e8dbfcd11..06516ab2fba9 100644
--- a/pkgs/development/ruby-modules/gem-config/default.nix
+++ b/pkgs/development/ruby-modules/gem-config/default.nix
@@ -203,7 +203,12 @@ in
   };
 
   eventmachine = attrs: {
+    dontBuild = false;
     buildInputs = [ openssl ];
+    postPatch = ''
+      substituteInPlace ext/em.cpp \
+        --replace 'if (bind (' 'if (::bind ('
+    '';
   };
 
   exif = attrs: {