diff --git a/deps/v8/include/v8-version.h b/deps/v8/include/v8-version.h
index f16596a58fa667..b026831a25cdd6 100644
--- a/deps/v8/include/v8-version.h
+++ b/deps/v8/include/v8-version.h
@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 12
 #define V8_MINOR_VERSION 4
 #define V8_BUILD_NUMBER 254
-#define V8_PATCH_LEVEL 14
+#define V8_PATCH_LEVEL 16
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)
diff --git a/deps/v8/infra/testing/builders.pyl b/deps/v8/infra/testing/builders.pyl
index 2aca712ca73f8a..7655763cab411c 100644
--- a/deps/v8/infra/testing/builders.pyl
+++ b/deps/v8/infra/testing/builders.pyl
@@ -962,7 +962,7 @@
   'v8_mac64_asan_rel': {
     'swarming_dimensions' : {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'v8testing', 'shards': 8},
@@ -971,7 +971,7 @@
   'v8_mac64_dbg': {
     'swarming_dimensions' : {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'mozilla'},
@@ -984,7 +984,7 @@
   'v8_mac_arm64_gc_stress_dbg': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'd8testing', 'test_args': ['--gc-stress'], 'shards': 3},
@@ -993,7 +993,7 @@
   'v8_mac64_noopt_dbg': {
     'swarming_dimensions' : {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'v8testing', 'shards': 6},
@@ -1002,7 +1002,7 @@
   'v8_mac64_rel': {
     'swarming_dimensions' : {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'mozilla'},
@@ -1015,7 +1015,7 @@
   'v8_mac_arm64_rel': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'pool': 'chromium.tests',
     },
     'tests': [
@@ -1031,7 +1031,7 @@
   'v8_mac_arm64_dbg': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'pool': 'chromium.tests',
     },
     'tests': [
@@ -1047,7 +1047,7 @@
   'v8_mac_arm64_full_dbg': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'pool': 'chromium.tests',
     },
     'tests': [
@@ -1063,7 +1063,7 @@
   'v8_mac_arm64_no_pointer_compression_dbg': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'pool': 'chromium.tests',
     },
     'tests': [
@@ -1848,7 +1848,7 @@
   'V8 Mac64': {
     'swarming_dimensions': {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'mozilla'},
@@ -1861,7 +1861,7 @@
   'V8 Mac64 - debug': {
     'swarming_dimensions': {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'mozilla'},
@@ -1874,7 +1874,7 @@
   'V8 Mac64 ASAN': {
     'swarming_dimensions': {
       'cpu': 'x86-64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'v8testing', 'shards': 10},
@@ -1883,7 +1883,7 @@
   'V8 Mac - arm64 - gc stress': {
     'swarming_dimensions': {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
     },
     'tests': [
       {'name': 'd8testing', 'test_args': ['--gc-stress'], 'shards': 3},
@@ -1891,7 +1891,7 @@
   },
   'V8 Mac - arm64': {
     'swarming_dimensions' : {
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'cpu': 'arm64',
       'pool': 'chromium.tests',
     },
@@ -1908,7 +1908,7 @@
   },
   'V8 Mac - arm64 - release': {
     'swarming_dimensions' : {
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'cpu': 'arm64',
       'pool': 'chromium.tests',
     },
@@ -1925,7 +1925,7 @@
   },
   'V8 Mac - arm64 - debug': {
     'swarming_dimensions' : {
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'cpu': 'arm64',
       'pool': 'chromium.tests',
     },
@@ -1943,7 +1943,7 @@
   'V8 Mac - arm64 - no pointer compression debug': {
     'swarming_dimensions' : {
       'cpu': 'arm64',
-      'os': 'Mac-13',
+      'os': 'Mac-14',
       'pool': 'chromium.tests',
     },
     'tests': [
diff --git a/deps/v8/src/objects/js-objects.cc b/deps/v8/src/objects/js-objects.cc
index e5a03dff14835e..2f3ab484cdc010 100644
--- a/deps/v8/src/objects/js-objects.cc
+++ b/deps/v8/src/objects/js-objects.cc
@@ -432,9 +432,7 @@ Maybe<bool> JSReceiver::SetOrCopyDataProperties(
       Nothing<bool>());
 
   if (!from->HasFastProperties() && target->HasFastProperties() &&
-      !IsJSGlobalProxy(*target)) {
-    // JSProxy is always in slow-mode.
-    DCHECK(!IsJSProxy(*target));
+      IsJSObject(*target) && !IsJSGlobalProxy(*target)) {
     // Convert to slow properties if we're guaranteed to overflow the number of
     // descriptors.
     int source_length;