diff --git a/python/ycm/tests/vimsupport_test.py b/python/ycm/tests/vimsupport_test.py
index bcc39709..19dae398 100644
--- a/python/ycm/tests/vimsupport_test.py
+++ b/python/ycm/tests/vimsupport_test.py
@@ -681,7 +681,7 @@ def _BuildLocations( start_line, start_column, end_line, end_column ):
 
 def ReplaceChunksInBuffer_SortedChunks_test():
   chunks = [
-    _BuildChunk( 1, 4, 1, 4, '('),
+    _BuildChunk( 1, 4, 1, 4, '(' ),
     _BuildChunk( 1, 11, 1, 11, ')' )
   ]
 
@@ -694,7 +694,7 @@ def ReplaceChunksInBuffer_SortedChunks_test():
 
 def ReplaceChunksInBuffer_UnsortedChunks_test():
   chunks = [
-    _BuildChunk( 1, 11, 1, 11, ')'),
+    _BuildChunk( 1, 11, 1, 11, ')' ),
     _BuildChunk( 1, 4, 1, 4, '(' )
   ]
 
@@ -1220,6 +1220,32 @@ def _BuildChunk( start_line,
   }
 
 
+@patch( 'vim.eval', new_callable = ExtendedMock )
+def AddDiagnosticSyntaxMatch_ErrorInMiddleOfLine_test( vim_eval ):
+  current_buffer = MockBuffer( [
+    'Highlight this error please'
+  ], 'some_file', 1 )
+
+  with patch( 'vim.current.buffer', current_buffer ):
+    vimsupport.AddDiagnosticSyntaxMatch( 1, 16, 1, 21 )
+
+  vim_eval.assert_called_once_with(
+    r"matchadd('YcmErrorSection', '\%1l\%16c\_.\{-}\%1l\%21c')" )
+
+
+@patch( 'vim.eval', new_callable = ExtendedMock )
+def AddDiagnosticSyntaxMatch_WarningAtEndOfLine_test( vim_eval ):
+  current_buffer = MockBuffer( [
+    'Highlight this warning'
+  ], 'some_file', 1 )
+
+  with patch( 'vim.current.buffer', current_buffer ):
+    vimsupport.AddDiagnosticSyntaxMatch( 1, 16, 1, 23, is_error = False )
+
+  vim_eval.assert_called_once_with(
+    r"matchadd('YcmWarningSection', '\%1l\%16c\_.\{-}\%1l\%23c')" )
+
+
 @patch( 'vim.command', new_callable=ExtendedMock )
 @patch( 'vim.current', new_callable=ExtendedMock)
 def WriteToPreviewWindow_test( vim_current, vim_command ):
diff --git a/python/ycm/vimsupport.py b/python/ycm/vimsupport.py
index 17f32e68..e1d750d7 100644
--- a/python/ycm/vimsupport.py
+++ b/python/ycm/vimsupport.py
@@ -208,29 +208,32 @@ def ClearYcmSyntaxMatches():
       vim.eval( 'matchdelete({0})'.format( match[ 'id' ] ) )
 
 
-# Returns the ID of the newly added match
-# Both line and column numbers are 1-based
 def AddDiagnosticSyntaxMatch( line_num,
                               column_num,
                               line_end_num = None,
                               column_end_num = None,
                               is_error = True ):
+  """Highlight a range in the current window starting from
+  (|line_num|, |column_num|) included to (|line_end_num|, |column_end_num|)
+  excluded. If |line_end_num| or |column_end_num| are not given, highlight the
+  character at (|line_num|, |column_num|). Both line and column numbers are
+  1-based. Return the ID of the newly added match."""
   group = 'YcmErrorSection' if is_error else 'YcmWarningSection'
 
-  if not line_end_num:
-    line_end_num = line_num
-
   line_num, column_num = LineAndColumnNumbersClamped( line_num, column_num )
-  line_end_num, column_end_num = LineAndColumnNumbersClamped( line_end_num,
-                                                              column_end_num )
 
-  if not column_end_num:
+  if not line_end_num or not column_end_num:
     return GetIntValue(
       "matchadd('{0}', '\%{1}l\%{2}c')".format( group, line_num, column_num ) )
-  else:
-    return GetIntValue(
-      "matchadd('{0}', '\%{1}l\%{2}c\_.\\{{-}}\%{3}l\%{4}c')".format(
-        group, line_num, column_num, line_end_num, column_end_num ) )
+
+  # -1 and then +1 to account for column end not included in the range.
+  line_end_num, column_end_num = LineAndColumnNumbersClamped(
+      line_end_num, column_end_num - 1 )
+  column_end_num += 1
+
+  return GetIntValue(
+    "matchadd('{0}', '\%{1}l\%{2}c\_.\\{{-}}\%{3}l\%{4}c')".format(
+      group, line_num, column_num, line_end_num, column_end_num ) )
 
 
 # Clamps the line and column numbers so that they are not past the contents of