diff --git a/common.gypi b/common.gypi
index 4ec9cf586803b8..5a2f34b6e058a2 100644
--- a/common.gypi
+++ b/common.gypi
@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.9',
+    'v8_embedder_string': '-node.10',
 
     ##### V8 defaults for Node.js #####
 
diff --git a/deps/v8/src/flags/flag-definitions.h b/deps/v8/src/flags/flag-definitions.h
index 2b807fedfc10cc..e20dd29fa59bb5 100644
--- a/deps/v8/src/flags/flag-definitions.h
+++ b/deps/v8/src/flags/flag-definitions.h
@@ -297,7 +297,6 @@ DEFINE_WEAK_IMPLICATION(harmony_rab_gsab_transfer, harmony_rab_gsab)
 #define HARMONY_SHIPPING_BASE(V)                                       \
   V(harmony_import_assertions, "harmony import assertions")            \
   V(harmony_change_array_by_copy, "harmony change-Array-by-copy")      \
-  V(harmony_string_is_well_formed, "harmony String#{is,to}WellFormed") \
   V(harmony_rab_gsab,                                                  \
     "harmony ResizableArrayBuffer / GrowableSharedArrayBuffer")        \
   V(harmony_regexp_unicode_sets, "harmony RegExp Unicode Sets")        \
diff --git a/deps/v8/src/init/bootstrapper.cc b/deps/v8/src/init/bootstrapper.cc
index 9c194809cbf8e0..9a582d2349a54e 100644
--- a/deps/v8/src/init/bootstrapper.cc
+++ b/deps/v8/src/init/bootstrapper.cc
@@ -2158,6 +2158,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           Builtin::kStringPrototypeIncludes, 1, false);
     SimpleInstallFunction(isolate_, prototype, "indexOf",
                           Builtin::kStringPrototypeIndexOf, 1, false);
+    SimpleInstallFunction(isolate(), prototype, "isWellFormed",
+                          Builtin::kStringPrototypeIsWellFormed, 0, false);
     SimpleInstallFunction(isolate_, prototype, "italics",
                           Builtin::kStringPrototypeItalics, 0, false);
     SimpleInstallFunction(isolate_, prototype, "lastIndexOf",
@@ -2214,6 +2216,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           Builtin::kStringPrototypeStartsWith, 1, false);
     SimpleInstallFunction(isolate_, prototype, "toString",
                           Builtin::kStringPrototypeToString, 0, true);
+    SimpleInstallFunction(isolate(), prototype, "toWellFormed",
+                          Builtin::kStringPrototypeToWellFormed, 0, false);
     SimpleInstallFunction(isolate_, prototype, "trim",
                           Builtin::kStringPrototypeTrim, 0, false);
 
@@ -5068,18 +5072,6 @@ void Genesis::InitializeGlobal_harmony_rab_gsab() {
                         Builtin::kSharedArrayBufferPrototypeGrow, 1, true);
 }
 
-void Genesis::InitializeGlobal_harmony_string_is_well_formed() {
-  if (!v8_flags.harmony_string_is_well_formed) return;
-  Handle<JSFunction> string_function(native_context()->string_function(),
-                                     isolate());
-  Handle<JSObject> string_prototype(
-      JSObject::cast(string_function->initial_map()->prototype()), isolate());
-  SimpleInstallFunction(isolate(), string_prototype, "isWellFormed",
-                        Builtin::kStringPrototypeIsWellFormed, 0, false);
-  SimpleInstallFunction(isolate(), string_prototype, "toWellFormed",
-                        Builtin::kStringPrototypeToWellFormed, 0, false);
-}
-
 void Genesis::InitializeGlobal_harmony_temporal() {
   if (!v8_flags.harmony_temporal) return;
   // -- T e m p o r a l