diff --git a/lib/vagrant/config/loader.rb b/lib/vagrant/config/loader.rb
index e3f80a579..ef4abe4bd 100644
--- a/lib/vagrant/config/loader.rb
+++ b/lib/vagrant/config/loader.rb
@@ -41,11 +41,21 @@ module Vagrant
       # `set` multiple times with the same name will override any previously
       # set values. In this way, the last set data for a given name wins.
       def set(name, sources)
-        @logger.info("Set #{name.inspect} = #{sources.inspect}")
-
         # Sources should be an array
         sources = [sources] if !sources.kind_of?(Array)
 
+        reliably_inspected_sources = sources.reduce({}) { |accum, source|
+          begin
+            accum[source] = source.inspect
+          rescue Encoding::CompatibilityError
+            accum[source] = "<!Vagrant failed to call #inspect source with object id #{source.object_id} and class #{source.class} due to a string encoding error>"
+          end
+
+          accum
+        }
+
+        @logger.info("Set #{name.inspect} = #{reliably_inspected_sources.values}")
+
         # Gather the procs for every source, since that is what we care about.
         procs = []
         sources.each do |source|
@@ -53,8 +63,8 @@ module Vagrant
             # Load the procs for this source and cache them. This caching
             # avoids the issue where a file may have side effects when loading
             # and loading it multiple times causes unexpected behavior.
-            @logger.debug("Populating proc cache for #{source.inspect}")
-            @proc_cache[source] = procs_for_source(source)
+            @logger.debug("Populating proc cache for #{reliably_inspected_sources[source]}")
+            @proc_cache[source] = procs_for_source(source, reliably_inspected_sources)
           end
 
           # Add on to the array of procs we're going to use
@@ -164,7 +174,7 @@ module Vagrant
       # The `Proc` objects returned will expect a single argument for
       # the configuration object and are expected to mutate this
       # configuration object.
-      def procs_for_source(source)
+      def procs_for_source(source, reliably_inspected_sources)
         # Convert all pathnames to strings so we just have their path
         source = source.to_s if source.is_a?(Pathname)
 
@@ -180,7 +190,7 @@ module Vagrant
           # Strings are considered paths, so load them
           return procs_for_path(source)
         else
-          raise ArgumentError, "Unknown configuration source: #{source.inspect}"
+          raise ArgumentError, "Unknown configuration source: #{reliably_inspected_sources[source]}"
         end
       end
 
diff --git a/test/unit/vagrant/config/loader_test.rb b/test/unit/vagrant/config/loader_test.rb
index cd7a9e975..4073b85db 100644
--- a/test/unit/vagrant/config/loader_test.rb
+++ b/test/unit/vagrant/config/loader_test.rb
@@ -38,6 +38,38 @@ describe Vagrant::Config::Loader do
 
   let(:instance) { described_class.new(versions, version_order) }
 
+  describe "#set" do
+    context "with an object that cannot be inspected" do
+
+      # This represents the euro symbol in UTF-16LE. pack("c*") returns an ASCII
+      # string and so we have to force the encoding
+      UTF_16LE_STRING_THAT_CANNOT_BE_DOWNCAST_TO_ASCII = [0x20, 0xAC].pack("c*").force_encoding("UTF-16LE")
+
+
+      let(:klass_with_bad_inspect_string) do
+        Class.new do
+          def inspect
+            UTF_16LE_STRING_THAT_CANNOT_BE_DOWNCAST_TO_ASCII
+          end
+        end
+      end
+
+      let(:test_source) {
+        Class.new do
+          def initialize(collaborator)
+            @foo = collaborator.new
+          end
+        end.new(klass_with_bad_inspect_string)
+      }
+
+      it "does not raise the ascii encoding exception" do
+        expect {
+          instance.set(:arbitrary, test_source)
+        }.to raise_error(ArgumentError, /Unknown configuration source/)
+      end
+    end
+  end
+
   describe "basic loading" do
     it "should ignore non-existent load order keys" do
       instance.load([:foo])