diff --git a/babel.config.js b/babel.config.js
index b55690d087..24dfc34ff2 100644
--- a/babel.config.js
+++ b/babel.config.js
@@ -102,14 +102,11 @@ module.exports = function (api) {
     ]
       .filter(Boolean)
       .map(normalize),
-    presets: [["@babel/env", envOpts]],
+    presets: [
+      ["@babel/env", envOpts],
+      ["@babel/preset-flow", { allowDeclareFields: true }],
+    ],
     plugins: [
-      // TODO: Use @babel/preset-flow when
-      // https://github.com/babel/babel/issues/7233 is fixed
-      [
-        "@babel/plugin-transform-flow-strip-types",
-        { allowDeclareFields: true },
-      ],
       [
         "@babel/proposal-object-rest-spread",
         { useBuiltIns: true, loose: true },
diff --git a/package.json b/package.json
index b3faa7e2e3..b094cec1dd 100644
--- a/package.json
+++ b/package.json
@@ -22,7 +22,6 @@
     "@babel/eslint-plugin-development-internal": "workspace:*",
     "@babel/plugin-proposal-dynamic-import": "^7.10.4",
     "@babel/plugin-proposal-object-rest-spread": "^7.11.0",
-    "@babel/plugin-transform-flow-strip-types": "^7.10.4",
     "@babel/plugin-transform-for-of": "^7.10.4",
     "@babel/plugin-transform-modules-commonjs": "^7.10.4",
     "@babel/plugin-transform-runtime": "^7.12.0",
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index ac9b6a9837..854119a2c3 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -33,10 +33,10 @@ export default class Printer {
     this._buf = new Buffer(map);
   }
 
-  format: Format;
+  declare format: Format;
   inForStatementInitCounter: number = 0;
 
-  _buf: Buffer;
+  declare _buf: Buffer;
   _printStack: Array<Node> = [];
   _indent: number = 0;
   _insideAux: boolean = false;
diff --git a/packages/babel-helper-module-imports/src/import-injector.js b/packages/babel-helper-module-imports/src/import-injector.js
index 1264dd4bc7..81acd472ae 100644
--- a/packages/babel-helper-module-imports/src/import-injector.js
+++ b/packages/babel-helper-module-imports/src/import-injector.js
@@ -98,17 +98,17 @@ export default class ImportInjector {
   /**
    * The path used for manipulation.
    */
-  _programPath: NodePath;
+  declare _programPath: NodePath;
 
   /**
    * The scope used to generate unique variable names.
    */
-  _programScope;
+  declare _programScope;
 
   /**
    * The file used to inject helpers and resolve paths.
    */
-  _hub;
+  declare _hub;
 
   /**
    * The default options to use with this instance when imports are added.
diff --git a/packages/babel-helper-replace-supers/src/index.js b/packages/babel-helper-replace-supers/src/index.js
index cc0eec0cfe..240e5b5504 100644
--- a/packages/babel-helper-replace-supers/src/index.js
+++ b/packages/babel-helper-replace-supers/src/index.js
@@ -272,14 +272,14 @@ export default class ReplaceSupers {
     this.opts = opts;
   }
 
-  file: HubInterface;
-  isDerivedConstructor: boolean;
-  isLoose: boolean;
-  isPrivateMethod: boolean;
-  isStatic: boolean;
-  methodPath: NodePath;
-  opts: ReplaceSupersOptions;
-  superRef: Object;
+  declare file: HubInterface;
+  declare isDerivedConstructor: boolean;
+  declare isLoose: boolean;
+  declare isPrivateMethod: boolean;
+  declare isStatic: boolean;
+  declare methodPath: NodePath;
+  declare opts: ReplaceSupersOptions;
+  declare superRef: Object;
 
   getObjectRef() {
     return t.cloneNode(this.opts.objectRef || this.opts.getObjectRef());
diff --git a/packages/babel-parser/src/parser/base.js b/packages/babel-parser/src/parser/base.js
index 770483e818..74c26a791b 100644
--- a/packages/babel-parser/src/parser/base.js
+++ b/packages/babel-parser/src/parser/base.js
@@ -10,23 +10,23 @@ import type ProductionParameterHandler from "../util/production-parameter";
 
 export default class BaseParser {
   // Properties set by constructor in index.js
-  options: Options;
-  inModule: boolean;
-  scope: ScopeHandler<*>;
-  classScope: ClassScopeHandler;
-  prodParam: ProductionParameterHandler;
-  expressionScope: ExpressionScopeHandler;
-  plugins: PluginsMap;
-  filename: ?string;
+  declare options: Options;
+  declare inModule: boolean;
+  declare scope: ScopeHandler<*>;
+  declare classScope: ClassScopeHandler;
+  declare prodParam: ProductionParameterHandler;
+  declare expressionScope: ExpressionScopeHandler;
+  declare plugins: PluginsMap;
+  declare filename: ?string;
   sawUnambiguousESM: boolean = false;
   ambiguousScriptDifferentAst: boolean = false;
 
   // Initialized by Tokenizer
-  state: State;
+  declare state: State;
   // input and length are not in state as they are constant and we do
   // not want to ever copy them, which happens if state gets cloned
-  input: string;
-  length: number;
+  declare input: string;
+  declare length: number;
 
   hasPlugin(name: string): boolean {
     return this.plugins.has(name);
diff --git a/packages/babel-parser/src/tokenizer/index.js b/packages/babel-parser/src/tokenizer/index.js
index 573db84a32..971226007c 100644
--- a/packages/babel-parser/src/tokenizer/index.js
+++ b/packages/babel-parser/src/tokenizer/index.js
@@ -101,11 +101,11 @@ export class Token {
     this.loc = new SourceLocation(state.startLoc, state.endLoc);
   }
 
-  type: TokenType;
-  value: any;
-  start: number;
-  end: number;
-  loc: SourceLocation;
+  declare type: TokenType;
+  declare value: any;
+  declare start: number;
+  declare end: number;
+  declare loc: SourceLocation;
 }
 
 // ## Tokenizer
diff --git a/packages/babel-parser/src/util/class-scope.js b/packages/babel-parser/src/util/class-scope.js
index 1ac00c995e..359af336e1 100644
--- a/packages/babel-parser/src/util/class-scope.js
+++ b/packages/babel-parser/src/util/class-scope.js
@@ -23,7 +23,7 @@ type raiseFunction = (number, string, ...any) => void;
 
 export default class ClassScopeHandler {
   stack: Array<ClassScope> = [];
-  raise: raiseFunction;
+  declare raise: raiseFunction;
   undefinedPrivateNames: Map<string, number> = new Map();
 
   constructor(raise: raiseFunction) {
diff --git a/packages/babel-parser/src/util/scope.js b/packages/babel-parser/src/util/scope.js
index 3d40c5fb87..b65cb7e0d9 100644
--- a/packages/babel-parser/src/util/scope.js
+++ b/packages/babel-parser/src/util/scope.js
@@ -39,8 +39,8 @@ type raiseFunction = (number, string, ...any) => void;
 // current scope in order to detect duplicate variable names.
 export default class ScopeHandler<IScope: Scope = Scope> {
   scopeStack: Array<IScope> = [];
-  raise: raiseFunction;
-  inModule: boolean;
+  declare raise: raiseFunction;
+  declare inModule: boolean;
   undefinedExports: Map<string, number> = new Map();
   undefinedPrivateNames: Map<string, number> = new Map();
 
diff --git a/packages/babel-traverse/src/context.js b/packages/babel-traverse/src/context.js
index 22b8bed959..5dd830f91d 100644
--- a/packages/babel-traverse/src/context.js
+++ b/packages/babel-traverse/src/context.js
@@ -11,10 +11,10 @@ export default class TraversalContext {
     this.opts = opts;
   }
 
-  parentPath: NodePath;
-  scope;
-  state;
-  opts;
+  declare parentPath: NodePath;
+  declare scope;
+  declare state;
+  declare opts;
   queue: ?Array<NodePath> = null;
 
   /**
diff --git a/packages/babel-traverse/src/path/index.js b/packages/babel-traverse/src/path/index.js
index a2eaf79f22..84f3664333 100644
--- a/packages/babel-traverse/src/path/index.js
+++ b/packages/babel-traverse/src/path/index.js
@@ -31,42 +31,30 @@ export default class NodePath {
   constructor(hub: HubInterface, parent: Object) {
     this.parent = parent;
     this.hub = hub;
-    this.contexts = [];
     this.data = null;
-    // this.shouldSkip = false; this.shouldStop = false; this.removed = false;
-    this._traverseFlags = 0;
-    this.state = null;
-    this.opts = null;
-    this.skipKeys = null;
-    this.parentPath = null;
+
     this.context = null;
-    this.container = null;
-    this.listKey = null;
-    this.key = null;
-    this.node = null;
     this.scope = null;
-    this.type = null;
   }
 
-  parent: Object;
-  hub: HubInterface;
-  contexts: Array<TraversalContext>;
-  data: Object;
-  shouldSkip: boolean;
-  shouldStop: boolean;
-  removed: boolean;
-  state: any;
-  opts: ?Object;
-  _traverseFlags: number;
-  skipKeys: ?Object;
-  parentPath: ?NodePath;
-  context: TraversalContext;
-  container: ?Object | Array<Object>;
-  listKey: ?string;
-  key: ?string;
-  node: ?Object;
-  scope: Scope;
-  type: ?string;
+  declare parent: Object;
+  declare hub: HubInterface;
+  declare data: Object;
+  declare context: TraversalContext;
+  declare scope: Scope;
+
+  contexts: Array<TraversalContext> = [];
+  state: any = null;
+  opts: ?Object = null;
+  // this.shouldSkip = false; this.shouldStop = false; this.removed = false;
+  _traverseFlags: number = 0;
+  skipKeys: ?Object = null;
+  parentPath: ?NodePath = null;
+  container: ?Object | Array<Object> = null;
+  listKey: ?string = null;
+  key: ?string = null;
+  node: ?Object = null;
+  type: ?string = null;
 
   static get({ hub, parentPath, parent, container, listKey, key }): NodePath {
     if (!hub && parentPath) {
diff --git a/packages/babel-traverse/src/scope/binding.js b/packages/babel-traverse/src/scope/binding.js
index 1f52201c51..341ecdfb6a 100644
--- a/packages/babel-traverse/src/scope/binding.js
+++ b/packages/babel-traverse/src/scope/binding.js
@@ -18,26 +18,19 @@ export default class Binding {
     this.path = path;
     this.kind = kind;
 
-    this.constantViolations = [];
-    this.constant = true;
-
-    this.referencePaths = [];
-    this.referenced = false;
-    this.references = 0;
-
     this.clearValue();
   }
 
-  constantViolations: Array<NodePath>;
-  constant: boolean;
+  constantViolations: Array<NodePath> = [];
+  constant: boolean = true;
 
-  referencePaths: Array<NodePath>;
-  referenced: boolean;
-  references: number;
+  referencePaths: Array<NodePath> = [];
+  referenced: boolean = false;
+  references: number = 0;
 
-  hasDeoptedValue: boolean;
-  hasValue: boolean;
-  value: any;
+  declare hasDeoptedValue: boolean;
+  declare hasValue: boolean;
+  declare value: any;
 
   deoptValue() {
     this.clearValue();
diff --git a/packages/babel-traverse/src/scope/lib/renamer.js b/packages/babel-traverse/src/scope/lib/renamer.js
index b15285e29c..528c43ef4d 100644
--- a/packages/babel-traverse/src/scope/lib/renamer.js
+++ b/packages/babel-traverse/src/scope/lib/renamer.js
@@ -37,9 +37,9 @@ export default class Renamer {
     this.binding = binding;
   }
 
-  oldName: string;
-  newName: string;
-  binding: Binding;
+  declare oldName: string;
+  declare newName: string;
+  declare binding: Binding;
 
   maybeConvertFromExportDeclaration(parentDeclar) {
     const maybeExportDeclar = parentDeclar.parentPath;
diff --git a/yarn.lock b/yarn.lock
index a816365276..5cb63b01e6 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -4575,7 +4575,6 @@ __metadata:
     "@babel/eslint-plugin-development-internal": "workspace:*"
     "@babel/plugin-proposal-dynamic-import": ^7.10.4
     "@babel/plugin-proposal-object-rest-spread": ^7.11.0
-    "@babel/plugin-transform-flow-strip-types": ^7.10.4
     "@babel/plugin-transform-for-of": ^7.10.4
     "@babel/plugin-transform-modules-commonjs": ^7.10.4
     "@babel/plugin-transform-runtime": ^7.12.0