diff --git a/crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md b/crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
new file mode 100644
index 0000000000..4a0d52ce98
--- /dev/null
+++ b/crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
@@ -0,0 +1,61 @@
+<!-- snapshot-diagnostics -->
+
+# Different ways that `UNSUPPORTED_BOOL_CONVERSION` can occur
+
+## Has a `__bool__` method, but has incorrect parameters
+
+```py
+class NotBoolable:
+    def __bool__(self, foo):
+        return False
+
+a = NotBoolable()
+
+# error: [unsupported-bool-conversion]
+10 and a and True
+```
+
+## Has a `__bool__` method, but has an incorrect return type
+
+```py
+class NotBoolable:
+    def __bool__(self) -> str:
+        return "wat"
+
+a = NotBoolable()
+
+# error: [unsupported-bool-conversion]
+10 and a and True
+```
+
+## Has a `__bool__` attribute, but it's not callable
+
+```py
+class NotBoolable:
+    __bool__: int = 3
+
+a = NotBoolable()
+
+# error: [unsupported-bool-conversion]
+10 and a and True
+```
+
+## Part of a union where at least one member has incorrect `__bool__` method
+
+```py
+class NotBoolable1:
+    def __bool__(self) -> str:
+        return "wat"
+
+class NotBoolable2:
+    pass
+
+class NotBoolable3:
+    __bool__: int = 3
+
+def get() -> NotBoolable1 | NotBoolable2 | NotBoolable3:
+    return NotBoolable2()
+
+# error: [unsupported-bool-conversion]
+10 and get() and True
+```
diff --git a/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_attribute,_but_it's_not_callable.snap b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_attribute,_but_it's_not_callable.snap
new file mode 100644
index 0000000000..2ef879a16f
--- /dev/null
+++ b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_attribute,_but_it's_not_callable.snap
@@ -0,0 +1,35 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: unsupported_bool_conversion.md - Different ways that `UNSUPPORTED_BOOL_CONVERSION` can occur - Has a `__bool__` attribute, but it's not callable
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | class NotBoolable:
+2 |     __bool__: int = 3
+3 | 
+4 | a = NotBoolable()
+5 | 
+6 | # error: [unsupported-bool-conversion]
+7 | 10 and a and True
+```
+
+# Diagnostics
+
+```
+error: lint:unsupported-bool-conversion: Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable
+ --> /src/mdtest_snippet.py:7:8
+  |
+6 | # error: [unsupported-bool-conversion]
+7 | 10 and a and True
+  |        ^
+  |
+
+```
diff --git a/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_an_incorrect_return_type.snap b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_an_incorrect_return_type.snap
new file mode 100644
index 0000000000..2b69db7bae
--- /dev/null
+++ b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_an_incorrect_return_type.snap
@@ -0,0 +1,36 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: unsupported_bool_conversion.md - Different ways that `UNSUPPORTED_BOOL_CONVERSION` can occur - Has a `__bool__` method, but has an incorrect return type
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | class NotBoolable:
+2 |     def __bool__(self) -> str:
+3 |         return "wat"
+4 | 
+5 | a = NotBoolable()
+6 | 
+7 | # error: [unsupported-bool-conversion]
+8 | 10 and a and True
+```
+
+# Diagnostics
+
+```
+error: lint:unsupported-bool-conversion: Boolean conversion is unsupported for type `NotBoolable`; the return type of its bool method (`str`) isn't assignable to `bool
+ --> /src/mdtest_snippet.py:8:8
+  |
+7 | # error: [unsupported-bool-conversion]
+8 | 10 and a and True
+  |        ^
+  |
+
+```
diff --git a/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_incorrect_parameters.snap b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_incorrect_parameters.snap
new file mode 100644
index 0000000000..a47dc7ee5f
--- /dev/null
+++ b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Has_a_`__bool__`_method,_but_has_incorrect_parameters.snap
@@ -0,0 +1,36 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: unsupported_bool_conversion.md - Different ways that `UNSUPPORTED_BOOL_CONVERSION` can occur - Has a `__bool__` method, but has incorrect parameters
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | class NotBoolable:
+2 |     def __bool__(self, foo):
+3 |         return False
+4 | 
+5 | a = NotBoolable()
+6 | 
+7 | # error: [unsupported-bool-conversion]
+8 | 10 and a and True
+```
+
+# Diagnostics
+
+```
+error: lint:unsupported-bool-conversion: Boolean conversion is unsupported for type `NotBoolable`; it incorrectly implements `__bool__`
+ --> /src/mdtest_snippet.py:8:8
+  |
+7 | # error: [unsupported-bool-conversion]
+8 | 10 and a and True
+  |        ^
+  |
+
+```
diff --git a/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Part_of_a_union_where_at_least_one_member_has_incorrect_`__bool__`_method.snap b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Part_of_a_union_where_at_least_one_member_has_incorrect_`__bool__`_method.snap
new file mode 100644
index 0000000000..8d33395fd2
--- /dev/null
+++ b/crates/red_knot_python_semantic/resources/mdtest/snapshots/unsupported_bool_conversion.md_-_Different_ways_that_`UNSUPPORTED_BOOL_CONVERSION`_can_occur_-_Part_of_a_union_where_at_least_one_member_has_incorrect_`__bool__`_method.snap
@@ -0,0 +1,43 @@
+---
+source: crates/red_knot_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: unsupported_bool_conversion.md - Different ways that `UNSUPPORTED_BOOL_CONVERSION` can occur - Part of a union where at least one member has incorrect `__bool__` method
+mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/unsupported_bool_conversion.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | class NotBoolable1:
+ 2 |     def __bool__(self) -> str:
+ 3 |         return "wat"
+ 4 | 
+ 5 | class NotBoolable2:
+ 6 |     pass
+ 7 | 
+ 8 | class NotBoolable3:
+ 9 |     __bool__: int = 3
+10 | 
+11 | def get() -> NotBoolable1 | NotBoolable2 | NotBoolable3:
+12 |     return NotBoolable2()
+13 | 
+14 | # error: [unsupported-bool-conversion]
+15 | 10 and get() and True
+```
+
+# Diagnostics
+
+```
+error: lint:unsupported-bool-conversion: Boolean conversion is unsupported for union `NotBoolable1 | NotBoolable2 | NotBoolable3` because `NotBoolable1` doesn't implement `__bool__` correctly
+  --> /src/mdtest_snippet.py:15:8
+   |
+14 | # error: [unsupported-bool-conversion]
+15 | 10 and get() and True
+   |        ^^^^^
+   |
+
+```
diff --git a/crates/red_knot_python_semantic/src/types.rs b/crates/red_knot_python_semantic/src/types.rs
index 695353ef7b..19195f561f 100644
--- a/crates/red_knot_python_semantic/src/types.rs
+++ b/crates/red_knot_python_semantic/src/types.rs
@@ -5670,12 +5670,11 @@ impl<'db> BoolError<'db> {
             Self::IncorrectArguments {
                 not_boolable_type, ..
             } => {
-                builder.into_diagnostic(
-                    format_args!(
-                        "Boolean conversion is unsupported for type `{}`; it incorrectly implements `__bool__`",
-                        not_boolable_type.display(context.db())
-                    ),
-                );
+                builder.into_diagnostic(format_args!(
+                    "Boolean conversion is unsupported for type `{}`; \
+                     it incorrectly implements `__bool__`",
+                    not_boolable_type.display(context.db())
+                ));
             }
             Self::IncorrectReturnType {
                 not_boolable_type,