diff --git a/CHANGES.md b/CHANGES.md
index f2290f41c09..8147382dea9 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -24,6 +24,7 @@
 - Address a missing case in the change to allow empty lines at the beginning of all
   blocks, except immediately before a docstring (#4130)
 - For stubs, fix logic to enforce empty line after nested classes with bodies (#4141)
+- Fix crash when using a walrus in a dictionary (#4155)
 
 ### Configuration
 
diff --git a/docs/usage_and_configuration/the_basics.md b/docs/usage_and_configuration/the_basics.md
index 4f9856c6a47..b541f07907c 100644
--- a/docs/usage_and_configuration/the_basics.md
+++ b/docs/usage_and_configuration/the_basics.md
@@ -268,6 +268,11 @@ recursive searches. An empty value means no paths are excluded. Use forward slas
 directories on all platforms (Windows, too). By default, Black also ignores all paths
 listed in `.gitignore`. Changing this value will override all default exclusions.
 
+If the regular expression contains newlines, it is treated as a
+[verbose regular expression](https://docs.python.org/3/library/re.html#re.VERBOSE). This
+is typically useful when setting these options in a `pyproject.toml` configuration file;
+see [Configuration format](#configuration-format) for more information.
+
 #### `--extend-exclude`
 
 Like `--exclude`, but adds additional files and directories on top of the default values
diff --git a/src/black/linegen.py b/src/black/linegen.py
index 4d468ce0f2e..9a3eb0ce73f 100644
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -242,7 +242,11 @@ def visit_dictsetmaker(self, node: Node) -> Iterator[Line]:
                 if i == 0:
                     continue
                 if node.children[i - 1].type == token.COLON:
-                    if child.type == syms.atom and child.children[0].type == token.LPAR:
+                    if (
+                        child.type == syms.atom
+                        and child.children[0].type == token.LPAR
+                        and not is_walrus_assignment(child)
+                    ):
                         if maybe_make_parens_invisible_in_atom(
                             child,
                             parent=node,
diff --git a/tests/data/cases/walrus_in_dict.py b/tests/data/cases/walrus_in_dict.py
new file mode 100644
index 00000000000..c33eecd84a6
--- /dev/null
+++ b/tests/data/cases/walrus_in_dict.py
@@ -0,0 +1,7 @@
+# flags: --preview
+{
+    "is_update": (up := commit.hash in update_hashes)
+}
+
+# output
+{"is_update": (up := commit.hash in update_hashes)}