diff --git a/deps/v8/include/v8-version.h b/deps/v8/include/v8-version.h
index 9ba8fc6d2ea4b7..c89f1e7fe01ba6 100644
--- a/deps/v8/include/v8-version.h
+++ b/deps/v8/include/v8-version.h
@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 9
 #define V8_MINOR_VERSION 0
 #define V8_BUILD_NUMBER 257
-#define V8_PATCH_LEVEL 19
+#define V8_PATCH_LEVEL 21
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)
diff --git a/deps/v8/src/compiler/js-call-reducer.cc b/deps/v8/src/compiler/js-call-reducer.cc
index 4bca26bbe0801a..b1405938ffe5c5 100644
--- a/deps/v8/src/compiler/js-call-reducer.cc
+++ b/deps/v8/src/compiler/js-call-reducer.cc
@@ -5380,24 +5380,31 @@ Reduction JSCallReducer::ReduceArrayPrototypePop(Node* node) {
       }
 
       // Compute the new {length}.
-      length = graph()->NewNode(simplified()->NumberSubtract(), length,
-                                jsgraph()->OneConstant());
+      Node* new_length = graph()->NewNode(simplified()->NumberSubtract(),
+                                          length, jsgraph()->OneConstant());
+
+      // This extra check exists solely to break an exploitation technique
+      // that abuses typer mismatches.
+      new_length = efalse = graph()->NewNode(
+          simplified()->CheckBounds(p.feedback(),
+                                    CheckBoundsFlag::kAbortOnOutOfBounds),
+          new_length, length, efalse, if_false);
 
       // Store the new {length} to the {receiver}.
       efalse = graph()->NewNode(
           simplified()->StoreField(AccessBuilder::ForJSArrayLength(kind)),
-          receiver, length, efalse, if_false);
+          receiver, new_length, efalse, if_false);
 
       // Load the last entry from the {elements}.
       vfalse = efalse = graph()->NewNode(
           simplified()->LoadElement(AccessBuilder::ForFixedArrayElement(kind)),
-          elements, length, efalse, if_false);
+          elements, new_length, efalse, if_false);
 
       // Store a hole to the element we just removed from the {receiver}.
       efalse = graph()->NewNode(
           simplified()->StoreElement(
               AccessBuilder::ForFixedArrayElement(GetHoleyElementsKind(kind))),
-          elements, length, jsgraph()->TheHoleConstant(), efalse, if_false);
+          elements, new_length, jsgraph()->TheHoleConstant(), efalse, if_false);
     }
 
     control = graph()->NewNode(common()->Merge(2), if_true, if_false);
@@ -5573,19 +5580,27 @@ Reduction JSCallReducer::ReduceArrayPrototypeShift(Node* node) {
         }
 
         // Compute the new {length}.
-        length = graph()->NewNode(simplified()->NumberSubtract(), length,
-                                  jsgraph()->OneConstant());
+        Node* new_length = graph()->NewNode(simplified()->NumberSubtract(),
+                                            length, jsgraph()->OneConstant());
+
+        // This extra check exists solely to break an exploitation technique
+        // that abuses typer mismatches.
+        new_length = etrue1 = graph()->NewNode(
+            simplified()->CheckBounds(p.feedback(),
+                                      CheckBoundsFlag::kAbortOnOutOfBounds),
+            new_length, length, etrue1, if_true1);
 
         // Store the new {length} to the {receiver}.
         etrue1 = graph()->NewNode(
             simplified()->StoreField(AccessBuilder::ForJSArrayLength(kind)),
-            receiver, length, etrue1, if_true1);
+            receiver, new_length, etrue1, if_true1);
 
         // Store a hole to the element we just removed from the {receiver}.
         etrue1 = graph()->NewNode(
             simplified()->StoreElement(AccessBuilder::ForFixedArrayElement(
                 GetHoleyElementsKind(kind))),
-            elements, length, jsgraph()->TheHoleConstant(), etrue1, if_true1);
+            elements, new_length, jsgraph()->TheHoleConstant(), etrue1,
+            if_true1);
       }
 
       Node* if_false1 = graph()->NewNode(common()->IfFalse(), branch1);
diff --git a/deps/v8/src/compiler/simplified-lowering.cc b/deps/v8/src/compiler/simplified-lowering.cc
index 49df06a0ec2ce0..903e8256f9e9d3 100644
--- a/deps/v8/src/compiler/simplified-lowering.cc
+++ b/deps/v8/src/compiler/simplified-lowering.cc
@@ -1474,10 +1474,15 @@ class RepresentationSelector {
     Type right_feedback_type = TypeOf(node->InputAt(1));
 
     // Using Signed32 as restriction type amounts to promising there won't be
-    // signed overflow. This is incompatible with relying on a Word32
-    // truncation in order to skip the overflow check.
+    // signed overflow. This is incompatible with relying on a Word32 truncation
+    // in order to skip the overflow check.  Similarly, we must not drop -0 from
+    // the result type unless we deopt for -0 inputs.
     Type const restriction =
-        truncation.IsUsedAsWord32() ? Type::Any() : Type::Signed32();
+        truncation.IsUsedAsWord32()
+            ? Type::Any()
+            : (truncation.identify_zeros() == kIdentifyZeros)
+                  ? Type::Signed32OrMinusZero()
+                  : Type::Signed32();
 
     // Handle the case when no int32 checks on inputs are necessary (but
     // an overflow check is needed on the output). Note that we do not