diff --git a/resources/test/fixtures/flake8_bugbear/B009_B010.py b/resources/test/fixtures/flake8_bugbear/B009_B010.py
index 611d6bc9df..623ddc6c96 100644
--- a/resources/test/fixtures/flake8_bugbear/B009_B010.py
+++ b/resources/test/fixtures/flake8_bugbear/B009_B010.py
@@ -1,7 +1,7 @@
 """
 Should emit:
-B009 - Line 18, 19, 20, 21, 22
-B010 - Line 33, 34, 35, 36
+B009 - Line 19, 20, 21, 22, 23, 24
+B010 - Line 40, 41, 42, 43, 44, 45
 """
 
 # Valid getattr usage
@@ -13,10 +13,12 @@ getattr(foo, bar, None)
 getattr(foo, "123abc")
 getattr(foo, r"123\abc")
 getattr(foo, "except")
+getattr(foo, "__123abc")
 
 # Invalid usage
 getattr(foo, "bar")
 getattr(foo, "_123abc")
+getattr(foo, "__123abc__")
 getattr(foo, "abc123")
 getattr(foo, r"abc123")
 _ = lambda x: getattr(x, "bar")
@@ -27,6 +29,7 @@ if getattr(x, "bar"):
 setattr(foo, bar, None)
 setattr(foo, "bar{foo}".format(foo="a"), None)
 setattr(foo, "123abc", None)
+setattr(foo, "__123abc", None)
 setattr(foo, r"123\abc", None)
 setattr(foo, "except", None)
 _ = lambda x: setattr(x, "bar", 1)
@@ -36,6 +39,7 @@ if setattr(x, "bar", 1):
 # Invalid usage
 setattr(foo, "bar", None)
 setattr(foo, "_123abc", None)
+setattr(foo, "__123abc__", None)
 setattr(foo, "abc123", None)
 setattr(foo, r"abc123", None)
 setattr(foo.bar, r"baz", None)
diff --git a/src/python/identifiers.rs b/src/python/identifiers.rs
index a93365c891..ff1ef5e70c 100644
--- a/src/python/identifiers.rs
+++ b/src/python/identifiers.rs
@@ -13,3 +13,12 @@ pub fn is_identifier(s: &str) -> bool {
     // Are the rest of the characters letters, digits, or underscores?
     s.chars().skip(1).all(|c| c.is_alphanumeric() || c == '_')
 }
+
+/// Returns `true` if a string is a private identifier, such that, when the
+/// identifier is defined in a class definition, it will be mangled prior to
+/// code generation.
+///
+/// See: <https://docs.python.org/3.5/reference/expressions.html?highlight=mangling#index-5>.
+pub fn is_mangled_private(id: &str) -> bool {
+    id.starts_with("__") && !id.ends_with("__")
+}
diff --git a/src/rules/flake8_bugbear/rules/getattr_with_constant.rs b/src/rules/flake8_bugbear/rules/getattr_with_constant.rs
index ae68e7145b..1b8b517ea1 100644
--- a/src/rules/flake8_bugbear/rules/getattr_with_constant.rs
+++ b/src/rules/flake8_bugbear/rules/getattr_with_constant.rs
@@ -4,7 +4,7 @@ use crate::ast::helpers::unparse_expr;
 use crate::ast::types::Range;
 use crate::checkers::ast::Checker;
 use crate::fix::Fix;
-use crate::python::identifiers::is_identifier;
+use crate::python::identifiers::{is_identifier, is_mangled_private};
 use crate::python::keyword::KWLIST;
 use crate::registry::Diagnostic;
 use crate::violations;
@@ -41,12 +41,13 @@ pub fn getattr_with_constant(checker: &mut Checker, expr: &Expr, func: &Expr, ar
     if !is_identifier(value) {
         return;
     }
-    if KWLIST.contains(&value.as_str()) {
+    if KWLIST.contains(&value.as_str()) || is_mangled_private(value.as_str()) {
         return;
     }
 
     let mut diagnostic =
         Diagnostic::new(violations::GetAttrWithConstant, Range::from_located(expr));
+
     if checker.patch(diagnostic.kind.rule()) {
         diagnostic.amend(Fix::replacement(
             unparse_expr(&attribute(obj, value), checker.stylist),
diff --git a/src/rules/flake8_bugbear/rules/setattr_with_constant.rs b/src/rules/flake8_bugbear/rules/setattr_with_constant.rs
index 8f63b90b90..74cf7d0393 100644
--- a/src/rules/flake8_bugbear/rules/setattr_with_constant.rs
+++ b/src/rules/flake8_bugbear/rules/setattr_with_constant.rs
@@ -4,7 +4,7 @@ use crate::ast::helpers::unparse_stmt;
 use crate::ast::types::Range;
 use crate::checkers::ast::Checker;
 use crate::fix::Fix;
-use crate::python::identifiers::is_identifier;
+use crate::python::identifiers::{is_identifier, is_mangled_private};
 use crate::python::keyword::KWLIST;
 use crate::registry::Diagnostic;
 use crate::source_code::Stylist;
@@ -51,7 +51,7 @@ pub fn setattr_with_constant(checker: &mut Checker, expr: &Expr, func: &Expr, ar
     if !is_identifier(name) {
         return;
     }
-    if KWLIST.contains(&name.as_str()) {
+    if KWLIST.contains(&name.as_str()) || is_mangled_private(name.as_str()) {
         return;
     }
     // We can only replace a `setattr` call (which is an `Expr`) with an assignment
@@ -61,6 +61,7 @@ pub fn setattr_with_constant(checker: &mut Checker, expr: &Expr, func: &Expr, ar
         if expr == child.as_ref() {
             let mut diagnostic =
                 Diagnostic::new(violations::SetAttrWithConstant, Range::from_located(expr));
+
             if checker.patch(diagnostic.kind.rule()) {
                 diagnostic.amend(Fix::replacement(
                     assignment(obj, name, value, checker.stylist),
diff --git a/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B009_B009_B010.py.snap b/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B009_B009_B010.py.snap
index 7262a6be77..80782d384e 100644
--- a/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B009_B009_B010.py.snap
+++ b/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B009_B009_B010.py.snap
@@ -5,109 +5,127 @@ expression: diagnostics
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 18
+    row: 19
     column: 0
   end_location:
-    row: 18
+    row: 19
     column: 19
   fix:
     content:
       - foo.bar
     location:
-      row: 18
+      row: 19
       column: 0
     end_location:
-      row: 18
+      row: 19
       column: 19
   parent: ~
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 19
+    row: 20
     column: 0
   end_location:
-    row: 19
+    row: 20
     column: 23
   fix:
     content:
       - foo._123abc
     location:
-      row: 19
+      row: 20
       column: 0
     end_location:
-      row: 19
+      row: 20
       column: 23
   parent: ~
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 20
+    row: 21
     column: 0
   end_location:
-    row: 20
+    row: 21
+    column: 26
+  fix:
+    content:
+      - foo.__123abc__
+    location:
+      row: 21
+      column: 0
+    end_location:
+      row: 21
+      column: 26
+  parent: ~
+- kind:
+    GetAttrWithConstant: ~
+  location:
+    row: 22
+    column: 0
+  end_location:
+    row: 22
     column: 22
   fix:
     content:
       - foo.abc123
     location:
-      row: 20
+      row: 22
       column: 0
     end_location:
-      row: 20
+      row: 22
       column: 22
   parent: ~
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 21
+    row: 23
     column: 0
   end_location:
-    row: 21
+    row: 23
     column: 23
   fix:
     content:
       - foo.abc123
     location:
-      row: 21
+      row: 23
       column: 0
     end_location:
-      row: 21
+      row: 23
       column: 23
   parent: ~
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 22
+    row: 24
     column: 14
   end_location:
-    row: 22
+    row: 24
     column: 31
   fix:
     content:
       - x.bar
     location:
-      row: 22
+      row: 24
       column: 14
     end_location:
-      row: 22
+      row: 24
       column: 31
   parent: ~
 - kind:
     GetAttrWithConstant: ~
   location:
-    row: 23
+    row: 25
     column: 3
   end_location:
-    row: 23
+    row: 25
     column: 20
   fix:
     content:
       - x.bar
     location:
-      row: 23
+      row: 25
       column: 3
     end_location:
-      row: 23
+      row: 25
       column: 20
   parent: ~
 
diff --git a/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B010_B009_B010.py.snap b/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B010_B009_B010.py.snap
index 12e6c2e844..878859b69d 100644
--- a/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B010_B009_B010.py.snap
+++ b/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B010_B009_B010.py.snap
@@ -5,91 +5,109 @@ expression: diagnostics
 - kind:
     SetAttrWithConstant: ~
   location:
-    row: 37
+    row: 40
     column: 0
   end_location:
-    row: 37
+    row: 40
     column: 25
   fix:
     content:
       - foo.bar = None
     location:
-      row: 37
+      row: 40
       column: 0
     end_location:
-      row: 37
+      row: 40
       column: 25
   parent: ~
 - kind:
     SetAttrWithConstant: ~
   location:
-    row: 38
+    row: 41
     column: 0
   end_location:
-    row: 38
+    row: 41
     column: 29
   fix:
     content:
       - foo._123abc = None
     location:
-      row: 38
+      row: 41
       column: 0
     end_location:
-      row: 38
+      row: 41
       column: 29
   parent: ~
 - kind:
     SetAttrWithConstant: ~
   location:
-    row: 39
+    row: 42
     column: 0
   end_location:
-    row: 39
+    row: 42
+    column: 32
+  fix:
+    content:
+      - foo.__123abc__ = None
+    location:
+      row: 42
+      column: 0
+    end_location:
+      row: 42
+      column: 32
+  parent: ~
+- kind:
+    SetAttrWithConstant: ~
+  location:
+    row: 43
+    column: 0
+  end_location:
+    row: 43
     column: 28
   fix:
     content:
       - foo.abc123 = None
     location:
-      row: 39
+      row: 43
       column: 0
     end_location:
-      row: 39
+      row: 43
       column: 28
   parent: ~
 - kind:
     SetAttrWithConstant: ~
   location:
-    row: 40
+    row: 44
     column: 0
   end_location:
-    row: 40
+    row: 44
     column: 29
   fix:
     content:
       - foo.abc123 = None
     location:
-      row: 40
+      row: 44
       column: 0
     end_location:
-      row: 40
+      row: 44
       column: 29
   parent: ~
 - kind:
     SetAttrWithConstant: ~
   location:
-    row: 41
+    row: 45
     column: 0
   end_location:
-    row: 41
+    row: 45
     column: 30
   fix:
     content:
       - foo.bar.baz = None
     location:
-      row: 41
+      row: 45
       column: 0
     end_location:
-      row: 41
+      row: 45
       column: 30
   parent: ~