diff --git a/sentry_sdk/utils.py b/sentry_sdk/utils.py
index 3889a7d15a..79448517e3 100644
--- a/sentry_sdk/utils.py
+++ b/sentry_sdk/utils.py
@@ -101,7 +101,7 @@
 """
 
 _LOCAL_IPS = frozenset({"127.0.0.1", "::1"})
-_LOCAL_DOMAINS = frozenset({"localhost", "127.0.0.1"})
+_LOCAL_DOMAINS = _LOCAL_IPS.union({"localhost"})
 
 
 def env_to_bool(value: "Any", *, strict: "Optional[bool]" = False) -> "bool | None":
@@ -2236,9 +2236,13 @@ def _is_localhost(
     if url_host is not None and _host_matches_local_domain(url_host):
         return True
 
-    for header_val in (host_header, forwarded_host_header):
-        if header_val is not None:
-            domain = header_val.split(":")[0]
+    for header in (host_header, forwarded_host_header):
+        if header is not None:
+            if header.startswith("["):
+                # Bracketed IPv6, e.g. [::1]:8080 or [::1]
+                domain = header.split("]")[0].strip("[]")
+            else:
+                domain = header.split(":")[0]
             if _host_matches_local_domain(domain):
                 return True
 
diff --git a/tests/test_utils.py b/tests/test_utils.py
index d3d70026e8..ffe3ae7046 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1425,6 +1425,7 @@ def test_package_version_is_none():
         # URL host (subdomain-aware matching)
         ({"url_host": "localhost"}, True),
         ({"url_host": "127.0.0.1"}, True),
+        ({"url_host": "::1"}, True),
         ({"url_host": "foo.localhost"}, True),
         ({"url_host": "bar.foo.localhost"}, True),
         ({"url_host": "foolocalhost"}, False),
@@ -1434,6 +1435,8 @@ def test_package_version_is_none():
         ({"host_header": "localhost"}, True),
         ({"host_header": "localhost:3000"}, True),
         ({"host_header": "127.0.0.1:8080"}, True),
+        ({"host_header": "[::1]"}, True),
+        ({"host_header": "[::1]:8080"}, True),
         ({"host_header": "foo.localhost"}, True),
         ({"host_header": "foo.localhost:8080"}, True),
         ({"host_header": "example.com"}, False),
@@ -1442,6 +1445,7 @@ def test_package_version_is_none():
         ({"forwarded_host_header": "localhost"}, True),
         ({"forwarded_host_header": "localhost:3000"}, True),
         ({"forwarded_host_header": "127.0.0.1:8080"}, True),
+        ({"forwarded_host_header": "[::1]:8080"}, True),
         ({"forwarded_host_header": "foo.localhost"}, True),
         ({"forwarded_host_header": "example.com"}, False),
         # No args