diff --git a/lib/bundler/gem_helper.rb b/lib/bundler/gem_helper.rb
index e7673cba88..55f484f723 100644
--- a/lib/bundler/gem_helper.rb
+++ b/lib/bundler/gem_helper.rb
@@ -74,7 +74,8 @@ module Bundler
 
     def build_gem
       file_name = nil
-      sh("gem build -V '#{spec_path}'") do
+      gem = ENV["BUNDLE_GEM"] ? ENV["BUNDLE_GEM"] : "gem"
+      sh("#{gem} build -V '#{spec_path}'") do
         file_name = File.basename(built_gem_path)
         SharedHelpers.filesystem_access(File.join(base, "pkg")) {|p| FileUtils.mkdir_p(p) }
         FileUtils.mv(built_gem_path, "pkg")
@@ -85,7 +86,8 @@ module Bundler
 
     def install_gem(built_gem_path = nil, local = false)
       built_gem_path ||= build_gem
-      out, _ = sh_with_code("gem install '#{built_gem_path}'#{" --local" if local}")
+      gem = ENV["BUNDLE_GEM"] ? ENV["BUNDLE_GEM"] : "gem"
+      out, _ = sh_with_code("#{gem} install '#{built_gem_path}'#{" --local" if local}")
       raise "Couldn't install gem, run `gem install #{built_gem_path}' for more detailed output" unless out[/Successfully installed/]
       Bundler.ui.confirm "#{name} (#{version}) installed."
     end
diff --git a/spec/bundler/commands/clean_spec.rb b/spec/bundler/commands/clean_spec.rb
index 158d58d67c..c18c7a195f 100644
--- a/spec/bundler/commands/clean_spec.rb
+++ b/spec/bundler/commands/clean_spec.rb
@@ -339,7 +339,8 @@ RSpec.describe "bundle clean" do
       gem "rack"
     G
 
-    sys_exec! "gem list"
+    gem = ruby_core? ? ENV["BUNDLE_GEM"] : "gem"
+    sys_exec! "#{gem} list"
     expect(out).to include("rack (1.0.0)").and include("thin (1.0)")
   end
 
@@ -461,8 +462,9 @@ RSpec.describe "bundle clean" do
     end
     bundle! :update, :all => bundle_update_requires_all?
 
-    sys_exec! "gem list"
-    expect(out).to include("foo (1.0.1, 1.0)")
+    gem = ruby_core? ? ENV["BUNDLE_GEM"] : "gem"
+    sys_exec! "#{gem} list"
+  expect(out).to include("foo (1.0.1, 1.0)")
   end
 
   it "cleans system gems when --force is used" do
@@ -485,7 +487,8 @@ RSpec.describe "bundle clean" do
     bundle "clean --force"
 
     expect(out).to include("Removing foo (1.0)")
-    sys_exec "gem list"
+    gem = ruby_core? ? ENV["BUNDLE_GEM"] : "gem"
+    sys_exec "#{gem} list"
     expect(out).not_to include("foo (1.0)")
     expect(out).to include("rack (1.0.0)")
   end
@@ -519,7 +522,8 @@ RSpec.describe "bundle clean" do
       expect(out).to include(system_gem_path.to_s)
       expect(out).to include("grant write permissions")
 
-      sys_exec "gem list"
+      gem = ruby_core? ? ENV["BUNDLE_GEM"] : "gem"
+      sys_exec "#{gem} list"
       expect(out).to include("foo (1.0)")
       expect(out).to include("rack (1.0.0)")
     end
diff --git a/spec/bundler/support/rubygems_ext.rb b/spec/bundler/support/rubygems_ext.rb
index c18f7650fc..42f887f268 100644
--- a/spec/bundler/support/rubygems_ext.rb
+++ b/spec/bundler/support/rubygems_ext.rb
@@ -59,10 +59,11 @@ module Spec
       no_reqs.map!(&:first)
       reqs.map! {|name, req| "'#{name}:#{req}'" }
       deps = reqs.concat(no_reqs).join(" ")
+      gem = Spec::Path.ruby_core? ? ENV["BUNDLE_GEM"] : "gem"
       cmd = if Gem::VERSION < "2.0.0"
-        "gem install #{deps} --no-rdoc --no-ri --conservative"
+        "#{gem} install #{deps} --no-rdoc --no-ri --conservative"
       else
-        "gem install #{deps} --no-document --conservative"
+        "#{gem} install #{deps} --no-document --conservative"
       end
       puts cmd
       system(cmd) || raise("Installing gems #{deps} for the tests to use failed!")