diff --git a/lib/vagrant/bundler.rb b/lib/vagrant/bundler.rb
index 8f3d7aceb..4d43501b0 100644
--- a/lib/vagrant/bundler.rb
+++ b/lib/vagrant/bundler.rb
@@ -19,13 +19,15 @@ module Vagrant
   # all Vagrant-installed plugins.
   class Bundler
 
+    # Location of HashiCorp gem repository
+    HASHICORP_GEMSTORE = "https://gems.hashicorp.com/".freeze
+
+    # Default gem repositories
     DEFAULT_GEM_SOURCES = [
       "https://rubygems.org/".freeze,
-      "https://gems.hashicorp.com/".freeze
+      HASHICORP_GEMSTORE
     ].freeze
 
-    HASHICORP_GEMSTORE = "https://gems.hashicorp.com/".freeze
-
     def self.instance
       @bundler ||= self.new
     end
@@ -262,6 +264,9 @@ module Vagrant
         @logger.debug("Adding source - #{src}")
         Gem.sources << src
       end
+
+      validate_configured_sources!
+
       source_list.values.each{|srcs| srcs.delete_if{|src| default_sources.include?(src)}}
       installer_set.prefer_sources = source_list
 
@@ -321,6 +326,27 @@ module Vagrant
       list.values
     end
 
+    # Iterates each configured RubyGem source to validate that it is properly
+    # available. If source is unavailable an exception is raised.
+    def validate_configured_sources!
+      Gem.sources.each_source do |src|
+        begin
+          src.load_specs(:released)
+        rescue Gem::Exception => source_error
+          if ENV["VAGRANT_ALLOW_PLUGIN_SOURCE_ERRORS"]
+            @logger.warn("Failed to load configured plugin source: #{src}!")
+            @logger.warn("Error received attempting to load source (#{src}): #{source_error}")
+            @logger.warn("Ignoring plugin source load failure due user request via env variable")
+          else
+            @logger.error("Failed to load configured plugin source `#{src}`: #{source_error}")
+            raise Vagrant::Errors::PluginSourceError,
+              source: src.uri.to_s,
+              error_msg: source_error.message
+          end
+        end
+      end
+    end
+
     # Generate the builtin resolver set
     def generate_builtin_set
       builtin_set = BuiltinSet.new
diff --git a/lib/vagrant/errors.rb b/lib/vagrant/errors.rb
index 7778d30ca..fbcad904f 100644
--- a/lib/vagrant/errors.rb
+++ b/lib/vagrant/errors.rb
@@ -596,6 +596,10 @@ module Vagrant
       error_key(:plugin_init_error)
     end
 
+    class PluginSourceError < VagrantError
+      error_key(:plugin_source_error)
+    end
+
     class PushesNotDefined < VagrantError
       error_key(:pushes_not_defined)
     end
diff --git a/plugins/commands/plugin/command/mixin_install_opts.rb b/plugins/commands/plugin/command/mixin_install_opts.rb
index 517b5158b..74e610be1 100644
--- a/plugins/commands/plugin/command/mixin_install_opts.rb
+++ b/plugins/commands/plugin/command/mixin_install_opts.rb
@@ -3,10 +3,7 @@ module VagrantPlugins
     module Command
       module MixinInstallOpts
         def build_install_opts(o, options)
-          options[:plugin_sources] = [
-            "https://rubygems.org",
-            "https://gems.hashicorp.com",
-          ]
+          options[:plugin_sources] = Vagrant::Bundler::DEFAULT_GEM_SOURCES.dup
 
           o.on("--entry-point NAME", String,
                "The name of the entry point file for loading the plugin.") do |entry_point|
diff --git a/plugins/commands/plugin/gem_helper.rb b/plugins/commands/plugin/gem_helper.rb
index c9a3dd4ed..1558b859e 100644
--- a/plugins/commands/plugin/gem_helper.rb
+++ b/plugins/commands/plugin/gem_helper.rb
@@ -43,7 +43,11 @@ module VagrantPlugins
         # Clear the sources so that installation uses custom sources
         old_sources = Gem.sources
         Gem.sources = Gem.default_sources
-        Gem.sources << "https://gems.hashicorp.com"
+        Vagrant::Bundler::DEFAULT_GEM_SOURCES.each do |source|
+          if !Gem.sources.include?(source)
+            Gem.sources << source
+          end
+        end
 
         # Use a silent UI so that we have no output
         Gem::DefaultUserInteraction.use_ui(Gem::SilentUI.new) do
diff --git a/templates/locales/en.yml b/templates/locales/en.yml
index 8b2a8f67a..aac75731f 100644
--- a/templates/locales/en.yml
+++ b/templates/locales/en.yml
@@ -1020,6 +1020,16 @@ en:
         You can however, install a plugin with the same name to replace
         these plugins. User-installed plugins take priority over
         system-installed plugins.
+      plugin_source_error: |-
+        Vagrant failed to load a configured plugin source. This can be caused
+        by a variety of issues including: transient connectivity issues, proxy
+        filtering rejecting access to a configured plugin source, or a configured
+        plugin source not responding correctly. Please review the error message
+        below to help resolve the issue:
+
+          %{error_msg}
+
+        Source: %{source}
       pushes_not_defined: |-
         The Vagrantfile does not define any 'push' strategies. In order to use
         `vagrant push`, you must define at least one push strategy:
@@ -1985,7 +1995,7 @@ en:
           untar_failure: |-
             The box failed to unpackage properly. Please verify that the box
             file you're trying to add is not corrupted and that enough disk space
-            is available and then try again. 
+            is available and then try again.
             The output from attempting to unpackage (if any):
 
             %{output}