diff --git a/pylsp/plugins/flake8_lint.py b/pylsp/plugins/flake8_lint.py
index 6be83b99..66aaaf36 100644
--- a/pylsp/plugins/flake8_lint.py
+++ b/pylsp/plugins/flake8_lint.py
@@ -174,7 +174,7 @@ def parse_stdout(document, stdout):
         # show also the code in message
         msg = code + ' ' + msg
         severity = lsp.DiagnosticSeverity.Warning
-        if code[0] == "E":
+        if code == "E999" or code[0] == "F":
             severity = lsp.DiagnosticSeverity.Error
         diagnostics.append(
             {
diff --git a/test/plugins/test_flake8_lint.py b/test/plugins/test_flake8_lint.py
index a72383ec..e9e7d216 100644
--- a/test/plugins/test_flake8_lint.py
+++ b/test/plugins/test_flake8_lint.py
@@ -39,7 +39,7 @@ def test_flake8_unsaved(workspace):
     assert unused_var['code'] == 'F841'
     assert unused_var['range']['start'] == {'line': 5, 'character': 1}
     assert unused_var['range']['end'] == {'line': 5, 'character': 11}
-    assert unused_var['severity'] == lsp.DiagnosticSeverity.Warning
+    assert unused_var['severity'] == lsp.DiagnosticSeverity.Error
 
 
 def test_flake8_lint(workspace):
@@ -53,7 +53,7 @@ def test_flake8_lint(workspace):
         assert unused_var['code'] == 'F841'
         assert unused_var['range']['start'] == {'line': 5, 'character': 1}
         assert unused_var['range']['end'] == {'line': 5, 'character': 11}
-        assert unused_var['severity'] == lsp.DiagnosticSeverity.Warning
+        assert unused_var['severity'] == lsp.DiagnosticSeverity.Error
     finally:
         os.remove(name)