diff --git a/autoload/youcompleteme.vim b/autoload/youcompleteme.vim
index 507b919d..b1554152 100644
--- a/autoload/youcompleteme.vim
+++ b/autoload/youcompleteme.vim
@@ -562,7 +562,6 @@ function! youcompleteme#OmniComplete( findstart, base )
 endfunction
 
 
-" TODO: Make this work again
 function! s:ShowDetailedDiagnostic()
   py ycm_state.ShowDetailedDiagnostic()
 endfunction
diff --git a/python/ycm/completers/cpp/clang_completer.py b/python/ycm/completers/cpp/clang_completer.py
index a8e5e676..c9e6d209 100644
--- a/python/ycm/completers/cpp/clang_completer.py
+++ b/python/ycm/completers/cpp/clang_completer.py
@@ -227,13 +227,11 @@ class ClangCompleter( Completer ):
     current_file = request_data[ 'filepath' ]
 
     if not self._diagnostic_store:
-      return responses.BuildDisplayMessageResponse(
-        NO_DIAGNOSTIC_MESSAGE )
+      raise ValueError( NO_DIAGNOSTIC_MESSAGE )
 
     diagnostics = self._diagnostic_store[ current_file ][ current_line ]
     if not diagnostics:
-      return responses.BuildDisplayMessageResponse(
-        NO_DIAGNOSTIC_MESSAGE )
+      raise ValueError( NO_DIAGNOSTIC_MESSAGE )
 
     closest_diagnostic = None
     distance_to_closest_diagnostic = 999
diff --git a/python/ycm/server/tests/basic_test.py b/python/ycm/server/tests/basic_test.py
index 5ff6a218..e09e6449 100644
--- a/python/ycm/server/tests/basic_test.py
+++ b/python/ycm/server/tests/basic_test.py
@@ -295,7 +295,8 @@ struct Foo {
 """
 
   filename = '/foo.cpp'
-  diag_data = {
+  event_data = {
+    'event_name': 'FileReadyToParse',
     'compilation_flags': ['-x', 'c++'],
     'line_num': 0,
     'column_num': 0,
@@ -309,17 +310,50 @@ struct Foo {
     }
   }
 
+  results = app.post_json( '/event_notification', event_data ).json
+  assert_that( results,
+               contains(
+                  has_entries( { 'text': contains_string( "expected ';'" ),
+                                 'line_num': 2,
+                                 'column_num': 7 } ) ) )
+
+
+@with_setup( Setup )
+def GetDetailedDiagnostic_ClangCompleter_Works_test():
+  app = TestApp( ycmd.app )
+  contents = """
+struct Foo {
+  int x  // semicolon missing here!
+  int y;
+  int c;
+  int d;
+};
+"""
+
+  filename = '/foo.cpp'
+  diag_data = {
+    'compilation_flags': ['-x', 'c++'],
+    'line_num': 2,
+    'column_num': 0,
+    'filetypes': ['cpp'],
+    'filepath': filename,
+    'file_data': {
+      filename: {
+        'contents': contents,
+        'filetypes': ['cpp']
+      }
+    }
+  }
+
   event_data = diag_data.copy()
   event_data.update( {
     'event_name': 'FileReadyToParse',
   } )
 
-  results = app.post_json( '/event_notification', event_data ).json
+  app.post_json( '/event_notification', event_data )
+  results = app.post_json( '/detailed_diagnostic', diag_data ).json
   assert_that( results,
-               contains(
-                  has_entries( { 'text': contains_string( "expected ';'" ),
-                                 'line_num': 2,
-                                 'column_num': 7 } ) ) )
+               has_entry( 'message', contains_string( "expected ';'" ) ) )
 
 
 @with_setup( Setup )
diff --git a/python/ycm/server/ycmd.py b/python/ycm/server/ycmd.py
index 8183cb89..50751b9a 100755
--- a/python/ycm/server/ycmd.py
+++ b/python/ycm/server/ycmd.py
@@ -133,6 +133,15 @@ def DefinedSubcommands():
   return _JsonResponse( completer.DefinedSubcommands() )
 
 
+@app.post( '/detailed_diagnostic')
+def GetDetailedDiagnostic():
+  LOGGER.info( 'Received detailed diagnostic request')
+  request_data = request.json
+  completer = _GetCompleterForRequestData( request_data )
+
+  return _JsonResponse( completer.GetDetailedDiagnostic( request_data ) )
+
+
 @app.post( '/debug_info')
 def DebugInfo():
   # This can't be at the top level because of possible extra conf preload
diff --git a/python/ycm/youcompleteme.py b/python/ycm/youcompleteme.py
index 66ebd111..ad46f12b 100644
--- a/python/ycm/youcompleteme.py
+++ b/python/ycm/youcompleteme.py
@@ -194,11 +194,11 @@ class YouCompleteMe( object ):
     return []
 
 
-  # TODO: Make this work again.
-  def GetDetailedDiagnostic( self ):
-    # if self.FiletypeCompletionUsable():
-    #   return self.GetFiletypeCompleter().GetDetailedDiagnostic()
-    pass
+  def ShowDetailedDiagnostic( self ):
+    debug_info = BaseRequest.PostDataToHandler( BuildRequestData(),
+                                                'detailed_diagnostic' )
+    if 'message' in debug_info:
+      vimsupport.EchoText( debug_info[ 'message' ] )
 
 
   def DebugInfo( self ):