diff --git a/.rubocop.yml b/.rubocop.yml
index 30e6b9ee..8346729e 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -61,3 +61,5 @@ Style/ParallelAssignment:
   Enabled: false
 Style/BlockDelimiters:
   Enabled: false
+Style/MultilineBlockChain:
+  Enabled: false
diff --git a/Gemfile b/Gemfile
index 90e9fd5b..295d773e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,6 +7,7 @@ gem 'yard', '~> 0.8', require: false
 # Test tools
 gem 'pry', '~> 0.10', group: :development, require: false
 gem 'pry-byebug'
+gem 'pry-stack_explorer'
 gem 'aruba', '~> 0.7.4', require: false
 gem 'rspec', '~> 3.0', require: false
 gem 'cucumber', '~> 2.0', require: false
diff --git a/middleman-core/fixtures/related-files-app/config.rb b/middleman-core/fixtures/related-files-app/config.rb
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/index.html.erb b/middleman-core/fixtures/related-files-app/source/index.html.erb
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/partials/_test.erb b/middleman-core/fixtures/related-files-app/source/partials/_test.erb
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/partials/_test2.haml b/middleman-core/fixtures/related-files-app/source/partials/_test2.haml
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/stylesheets/_include3.sass b/middleman-core/fixtures/related-files-app/source/stylesheets/_include3.sass
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/stylesheets/_include4.scss b/middleman-core/fixtures/related-files-app/source/stylesheets/_include4.scss
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/stylesheets/include1.css b/middleman-core/fixtures/related-files-app/source/stylesheets/include1.css
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/stylesheets/include2.css.scss b/middleman-core/fixtures/related-files-app/source/stylesheets/include2.css.scss
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/related-files-app/source/stylesheets/site.css.scss b/middleman-core/fixtures/related-files-app/source/stylesheets/site.css.scss
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/lib/middleman-core/sitemap/store.rb b/middleman-core/lib/middleman-core/sitemap/store.rb
index 2d1e052d..7a0a8736 100644
--- a/middleman-core/lib/middleman-core/sitemap/store.rb
+++ b/middleman-core/lib/middleman-core/sitemap/store.rb
@@ -180,7 +180,7 @@ module Middleman
       Contract String => String
       def extensionless_path(file)
         path = file.dup
-        remove_templating_extensions(path)
+        ::Middleman::Util.remove_templating_extensions(path)
       end
 
       # Actually update the resource list, assuming anything has called
@@ -224,16 +224,6 @@ module Middleman
         end
       end
 
-      # Removes the templating extensions, while keeping the others
-      # @param [String] path
-      # @return [String]
-      Contract String => String
-      def remove_templating_extensions(path)
-        # Strip templating extensions as long as Tilt knows them
-        path = path.sub(/#{::Regexp.escape(File.extname(path))}$/, '') while ::Tilt[path]
-        path
-      end
-
       # Remove the locale token from the end of the path
       # @param [String] path
       # @return [String]
diff --git a/middleman-core/lib/middleman-core/sources/source_watcher.rb b/middleman-core/lib/middleman-core/sources/source_watcher.rb
index ff18c6f9..85234816 100644
--- a/middleman-core/lib/middleman-core/sources/source_watcher.rb
+++ b/middleman-core/lib/middleman-core/sources/source_watcher.rb
@@ -225,15 +225,23 @@ module Middleman
     # @return [void]
     Contract ArrayOf[Pathname], ArrayOf[Pathname] => Any
     def update(updated_paths, removed_paths)
-      valid_updates = (updated_paths | find_related_files(updated_paths + removed_paths))
-                      .lazy
-                      .map(&method(:path_to_source_file))
+      valid_updates = updated_paths
+                      .map { |p| ::Middleman::Util.path_to_source_file(p, @directory, @type) }
                       .select(&method(:valid?))
-                      .to_a
-                      .each do |f|
-                        add_file_to_cache(f)
-                        logger.debug "== Change (#{f[:types].inspect}): #{f[:relative_path]}"
-                      end
+
+      valid_updates.each do |f|
+        add_file_to_cache(f)
+        logger.debug "== Change (#{f[:types].inspect}): #{f[:relative_path]}"
+      end
+
+      related_updates = ::Middleman::Util.find_related_files(app, (updated_paths + removed_paths)).select(&method(:valid?))
+
+      related_updates.each do |f|
+        add_file_to_cache(f)
+        logger.debug "== Possible Change (#{f[:types].inspect}): #{f[:relative_path]}"
+      end
+
+      valid_updates |= related_updates
 
       valid_removes = removed_paths
                       .lazy
@@ -283,35 +291,5 @@ module Middleman
         @only.any? { |reg| reg.match(file[:relative_path].to_s) }
       end
     end
-
-    # Convert a path to a file resprentation.
-    #
-    # @param [Pathname] path The path.
-    # @return [Middleman::SourceFile]
-    Contract Pathname => IsA['Middleman::SourceFile']
-    def path_to_source_file(path)
-      types = Set.new([@type])
-
-      relative_path   = path.relative_path_from(@directory)
-      destination_dir = @options.fetch(:destination_dir, false)
-      relative_path   = File.join(destination_dir, relative_path) if destination_dir
-
-      ::Middleman::SourceFile.new(Pathname(relative_path), path, @directory, types)
-    end
-
-    # Finds files which should also be considered to be dirty when
-    # the given file(s) are touched.
-    #
-    # @param [Pathname] files The original touched file paths.
-    # @return [Pathname] All related file paths, not including the source file paths.
-    Contract ArrayOf[Pathname] => ArrayOf[Pathname]
-    def find_related_files(files)
-      files.flat_map do |file|
-        # If any partial file changes, reload all non-partials
-        if File.basename(file).start_with?('_')
-          Dir[File.join(@directory, app.config[:source], "**/[^_]*.#{File.extname(file)}")].map { |p| Pathname(p) }
-        end
-      end.compact.uniq - files
-    end
   end
 end
diff --git a/middleman-core/lib/middleman-core/util.rb b/middleman-core/lib/middleman-core/util.rb
index 139bca08..15964b17 100644
--- a/middleman-core/lib/middleman-core/util.rb
+++ b/middleman-core/lib/middleman-core/util.rb
@@ -430,6 +430,95 @@ module Middleman
       end
     end
 
+    Contract String => String
+    def step_through_extensions(path)
+      while ::Tilt[path]
+        yield File.extname(path) if block_given?
+
+        # Strip templating extensions as long as Tilt knows them
+        path = path.sub(/#{::Regexp.escape(File.extname(path))}$/, '')
+      end
+
+      yield File.extname(path) if block_given?
+
+      path
+    end
+
+    # Removes the templating extensions, while keeping the others
+    # @param [String] path
+    # @return [String]
+    Contract String => String
+    def remove_templating_extensions(path)
+      step_through_extensions(path)
+    end
+
+    # Removes the templating extensions, while keeping the others
+    # @param [String] path
+    # @return [String]
+    Contract String => ArrayOf[String]
+    def collect_extensions(path)
+      result = []
+
+      step_through_extensions(path) { |e| result << e }
+
+      result
+    end
+
+    # Convert a path to a file resprentation.
+    #
+    # @param [Pathname] path The path.
+    # @return [Middleman::SourceFile]
+    Contract Pathname, Pathname, Symbol => IsA['Middleman::SourceFile']
+    def path_to_source_file(path, directory, type)
+      types = Set.new([type])
+
+      relative_path = path.relative_path_from(directory)
+      # destination_dir = @options.fetch(:destination_dir, false)
+      # relative_path   = File.join(destination_dir, relative_path) if destination_dir
+
+      ::Middleman::SourceFile.new(Pathname(relative_path), path, directory, types)
+    end
+
+    # Finds files which should also be considered to be dirty when
+    # the given file(s) are touched.
+    #
+    # @param [Middleman::Application] app The app.
+    # @param [Pathname] files The original touched file paths.
+    # @return [Middleman::SourceFile] All related file paths, not including the source file paths.
+    Contract IsA['Middleman::Application'], ArrayOf[Pathname] => ArrayOf[IsA['Middleman::SourceFile']]
+    def find_related_files(app, files)
+      all_extensions = files.flat_map { |f| collect_extensions(f.to_s) }
+
+      sass_type_aliasing = ['.scss', '.sass']
+      erb_type_aliasing = ['.erb', '.haml', '.slim']
+
+      if (all_extensions & sass_type_aliasing).length > 0
+        all_extensions |= sass_type_aliasing
+      end
+
+      if (all_extensions & erb_type_aliasing).length > 0
+        all_extensions |= erb_type_aliasing
+      end
+
+      all_extensions.uniq!
+
+      app.sitemap.resources.select { |r|
+        local_extensions = collect_extensions(r.file_descriptor[:relative_path].to_s)
+
+        if (local_extensions & sass_type_aliasing).length > 0
+          local_extensions |= sass_type_aliasing
+        end
+
+        if (local_extensions & erb_type_aliasing).length > 0
+          local_extensions |= erb_type_aliasing
+        end
+
+        local_extensions.uniq!
+
+        ((all_extensions & local_extensions).length > 0) && files.none? { |f| f == r.file_descriptor[:full_path] }
+      }.map(&:file_descriptor)
+    end
+
     # Handy methods for dealing with URI templates. Mix into whatever class.
     module UriTemplates
       module_function
diff --git a/middleman-core/spec/middleman-core/util_spec.rb b/middleman-core/spec/middleman-core/util_spec.rb
index f50d7555..ccac1885 100644
--- a/middleman-core/spec/middleman-core/util_spec.rb
+++ b/middleman-core/spec/middleman-core/util_spec.rb
@@ -141,4 +141,44 @@ describe Middleman::Util do
 
   end
 
+  describe "::find_related_files" do
+    after(:each) do
+      Given.cleanup!
+    end
+
+    before(:each) do
+      Given.fixture 'related-files-app'
+      @mm = Middleman::Application.new
+    end
+
+    def source_file(path)
+      Pathname(File.expand_path("source/#{path}"))
+    end
+
+    it "Finds partials possibly related to ERb files" do
+      related = Middleman::Util.find_related_files(@mm, [source_file('partials/_test.erb')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/index.html.erb")
+
+      related = Middleman::Util.find_related_files(@mm, [source_file('partials/_test2.haml')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/index.html.erb")
+    end
+
+    it "Finds partials possible related to Scss files" do
+      related = Middleman::Util.find_related_files(@mm, [source_file('stylesheets/_include4.scss')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/stylesheets/site.css.scss")
+      expect(related).to include File.expand_path("source/stylesheets/include2.css.scss")
+
+      related = Middleman::Util.find_related_files(@mm, [source_file('stylesheets/include2.css.scss')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/stylesheets/site.css.scss")
+      expect(related).not_to include File.expand_path("source/stylesheets/include2.css.scss")
+
+      related = Middleman::Util.find_related_files(@mm, [source_file('stylesheets/include1.css')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/stylesheets/site.css.scss")
+      expect(related).to include File.expand_path("source/stylesheets/include2.css.scss")
+
+      related = Middleman::Util.find_related_files(@mm, [source_file('stylesheets/_include3.sass')]).map { |f| f[:full_path].to_s }
+      expect(related).to include File.expand_path("source/stylesheets/site.css.scss")
+      expect(related).to include File.expand_path("source/stylesheets/include2.css.scss")
+    end
+  end
 end