diff --git a/lib/pdk/cli/exec.rb b/lib/pdk/cli/exec.rb
index dac74edc9..dcc3d0d1d 100644
--- a/lib/pdk/cli/exec.rb
+++ b/lib/pdk/cli/exec.rb
@@ -121,6 +121,24 @@ def update_environment(additional_env)
           @environment.merge!(additional_env)
         end
 
+        def check_for_legacy_env_vars
+          if ENV['PUPPET_GEM_VERSION']
+            PDK.logger.warn_once _(
+              'PUPPET_GEM_VERSION is not supported by PDK. ' \
+              'Please use the --puppet-version option on your PDK command ' \
+              'or set the PDK_PUPPET_VERSION environment variable instead',
+            )
+            @process.environment['PUPPET_GEM_VERSION'] = nil
+          end
+
+          %w[FACTER HIERA].each do |gem|
+            if ENV["#{gem}_GEM_VERSION"]
+              PDK.logger.warn_once _("#{gem}_GEM_VERSION is not supported by PDK.")
+              @process.environment["#{gem}_GEM_VERSION"] = nil
+            end
+          end
+        end
+
         def execute!
           # Start spinning if configured.
           @spinner.auto_spin if @spinner
@@ -130,6 +148,8 @@ def execute!
             @process.environment[k] = v
           end
 
+          check_for_legacy_env_vars
+
           @process.environment['BUNDLE_IGNORE_CONFIG'] = '1'
 
           if [:module, :pwd].include?(context)
diff --git a/lib/pdk/logger.rb b/lib/pdk/logger.rb
index 1f5784cec..32c5911b3 100644
--- a/lib/pdk/logger.rb
+++ b/lib/pdk/logger.rb
@@ -10,6 +10,7 @@ class Logger < ::Logger
 
     def initialize
       super(STDERR)
+      @sent_messages = {}
 
       # TODO: Decide on output format.
       self.formatter = proc do |severity, _datetime, _progname, msg|
@@ -29,6 +30,13 @@ def initialize
       self.level = ::Logger::INFO
     end
 
+    def warn_once(*args)
+      hash = args.inspect.hash
+      return if (@sent_messages[::Logger::WARN] ||= {}).key?(hash)
+      @sent_messages[::Logger::WARN][hash] = true
+      warn(*args)
+    end
+
     def enable_debug_output
       self.level = ::Logger::DEBUG
     end
diff --git a/spec/acceptance/version_changer_spec.rb b/spec/acceptance/version_changer_spec.rb
index f02420a24..9e1a3973c 100644
--- a/spec/acceptance/version_changer_spec.rb
+++ b/spec/acceptance/version_changer_spec.rb
@@ -4,6 +4,23 @@
   context 'in a new module' do
     include_context 'in a new module', 'version_select'
 
+    %w[PUPPET FACTER HIERA].each do |gem|
+      context "when the legacy #{gem}_GEM_VERSION environment variable is used" do
+        if Gem.win_platform?
+          pre_cmd = "$env:#{gem}_GEM_VERSION='1.0.0';"
+          post_cmd = "; remove-item env:\\#{gem}_GEM_VERSION"
+        else
+          pre_cmd = "#{gem}_GEM_VERSION=1.0.0"
+          post_cmd = ''
+        end
+
+        describe command("#{pre_cmd} pdk validate#{post_cmd}") do
+          its(:exit_status) { is_expected.to eq(0) }
+          its(:stderr) { is_expected.to match(%r{#{gem}_GEM_VERSION is not supported by PDK}im) }
+        end
+      end
+    end
+
     %w[5.5.0 4.10.10].each do |puppet_version|
       describe command("pdk validate --puppet-version #{puppet_version}") do
         its(:exit_status) { is_expected.to eq(0) }
diff --git a/spec/unit/pdk/logger_spec.rb b/spec/unit/pdk/logger_spec.rb
index 665d43db9..4eba7ca7c 100644
--- a/spec/unit/pdk/logger_spec.rb
+++ b/spec/unit/pdk/logger_spec.rb
@@ -32,4 +32,13 @@
 
     it { is_expected.to have_attributes(debug?: true) }
   end
+
+  describe '#warn_once' do
+    it 'only sends each message once' do
+      expect(STDERR).to receive(:write).with("pdk (WARN): message 1\n").once
+
+      pdk_logger.warn_once('message 1')
+      pdk_logger.warn_once('message 1')
+    end
+  end
 end