diff --git a/src/elvis_style.erl b/src/elvis_style.erl
index 1431170..52fe1e7 100644
--- a/src/elvis_style.erl
+++ b/src/elvis_style.erl
@@ -195,7 +195,7 @@ default(no_common_caveats_call) ->
            {timer, send_interval, 3},
            {erlang, size, 1}]};
 default(atom_naming_convention) ->
-    #{regex => "^([a-z][a-z0-9]*_?)*(_SUITE)?$", enclosed_atoms => ".*"};
+    #{regex => "^[a-z](_?[a-z0-9]+)*(_SUITE)?$", enclosed_atoms => ".*"};
 %% Not restrictive. Those who want more restrictions can set it like "^[^_]*$"
 default(numeric_format) ->
     #{regex => ".*",
diff --git a/test/examples/fail_atom_naming_convention.erl b/test/examples/fail_atom_naming_convention.erl
index 7cf7f50..2d75f84 100644
--- a/test/examples/fail_atom_naming_convention.erl
+++ b/test/examples/fail_atom_naming_convention.erl
@@ -12,4 +12,12 @@ for_test() ->
     '\'\'',
     '\'startswithbacktick',
     'backtick\'inside',
-    'backtick at the end\''.
+    'backtick at the end\'',
+    non200_,
+    '__', % invalid, even when '_' is actually valid
+    two_underscores__together_are_not_valid,
+    '_something', % invalid because it starts with underscore
+    '42_invalid_because_it_starts_with_a_number',
+    '42invalid', %% even without underscores
+    weDontSupportCamelCaseHere,
+    not_even_in_a__SUITE.
diff --git a/test/examples/pass_atom_naming_convention.erl b/test/examples/pass_atom_naming_convention.erl
index d650e0a..9536ef8 100644
--- a/test/examples/pass_atom_naming_convention.erl
+++ b/test/examples/pass_atom_naming_convention.erl
@@ -5,4 +5,10 @@
 for_test() ->
     this_is_an_ok_atom,
     'and_so_is_this',
-    'and_this_1_too'.
+    'and_this_1_too',
+    non_200,
+    '_', % used by ets/mnesia/etc.
+    non200, % valid, even without underscores
+    valid_200even_if_numb3rs_appear_between_letters,
+    blahblah_SUITE,
+    x.
diff --git a/test/style_SUITE.erl b/test/style_SUITE.erl
index c59f94e..10b1a1e 100644
--- a/test/style_SUITE.erl
+++ b/test/style_SUITE.erl
@@ -1302,7 +1302,7 @@ verify_atom_naming_convention(Config) ->
     Group = proplists:get_value(group, Config, erl_files),
     Ext = proplists:get_value(test_file_ext, Config, "erl"),
 
-    BaseRegex = "^([a-z][a-z0-9_]+)$",
+    BaseRegex = "^[a-z](_?[a-z0-9]+)*(_SUITE)?$",
 
     % pass
     PassModule = pass_atom_naming_convention,
@@ -1337,37 +1337,37 @@ verify_atom_naming_convention(Config) ->
     FailModule2 = fail_atom_naming_convention_exception_class,
     FailPath2 = atom_to_list(FailModule2) ++ "." ++ Ext,
 
-    [_, _, _, _, _, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => BaseRegex, enclosed_atoms => same},
                               FailPath),
-    [_, _, _, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => "^([a-zA-Z_]+)$", enclosed_atoms => same},
                               FailPath),
-    [_, _] =
+    [_, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => "^([a-zA-Z_' \\\\]+)$", enclosed_atoms => same},
                               FailPath),
-    [_, _, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => "^([a-zA-Z\-_]+)$", enclosed_atoms => same},
                               FailPath),
-    [_] =
+    [_, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => "^([a-zA-Z\-_' \\\\]+)$", enclosed_atoms => same},
                               FailPath),
-    [] =
+    [_] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
@@ -1380,26 +1380,26 @@ verify_atom_naming_convention(Config) ->
                               #{regex => BaseRegex, ignore => [FailModule]},
                               FailPath),
     KeepRegex = "^([a-zA-Z0-9_]+)$",
-    [_, _, _, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => KeepRegex, enclosed_atoms => "^([a-z][a-z0-9A-Z_]*)$"},
                               FailPath),
-    [_, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => KeepRegex,
                                 enclosed_atoms => "^([a-z][a-z0-9A-Z_' \\\\]*)$"},
                               FailPath),
-    [_, _, _, _, _, _, _] =
+    [_, _, _, _, _, _, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
                               #{regex => KeepRegex, enclosed_atoms => "^([a-z][\-a-z0-9A-Z_]*)$"},
                               FailPath),
-    [_, _, _, _] =
+    [_, _, _, _, _, _] =
         elvis_core_apply_rule(Config,
                               elvis_style,
                               atom_naming_convention,
@@ -1414,7 +1414,7 @@ verify_atom_naming_convention(Config) ->
                               FailPath2),
     _ = case Group of
             beam_files -> % 'or_THIS' getting stripped of enclosing '
-                [_, _, _, _] =
+                [_, _, _, _, _, _, _, _] =
                     elvis_core_apply_rule(Config,
                                           elvis_style,
                                           atom_naming_convention,
@@ -1422,7 +1422,7 @@ verify_atom_naming_convention(Config) ->
                                             enclosed_atoms => "^([\\\\][\-a-z0-9A-Z_' \\\\]*)$"},
                                           FailPath);
             erl_files ->
-                [_, _, _, _, _] =
+                [_, _, _, _, _, _, _, _, _] =
                     elvis_core_apply_rule(Config,
                                           elvis_style,
                                           atom_naming_convention,