Cannot redeclare block-scoped variable 'ngDevMode'

My app in on Angular 5. Here is how the package.json looks like

{
"name": "myapp",
"version": "0.0.0",
"license": "MIT",
"scripts": {
"ng": "ng",
"start": "ng serve",
"build": "ng build --prod",
"test": "ng test",
"lint": "ng lint",
"e2e": "ng e2e"
},
"private": true,
"dependencies": {
"@angular/animations": "^5.2.0",
"@angular/common": "^5.2.0",
"@angular/compiler": "^5.2.0",
"@angular/core": "^5.2.0",
"@angular/forms": "^5.2.0",
"@angular/http": "^5.2.0",
"@angular/platform-browser": "^5.2.0",
"@angular/platform-browser-dynamic": "^5.2.0",
"@angular/router": "^5.2.0",
"@types/file-saver": "0.0.1",
"angular-2-dropdown-multiselect": "^1.6.0",
"angular2-csv": "^0.2.5",
"bootstrap": "^3.3.7",
"core-js": "^2.4.1",
"file-saver": "^1.3.3",
"ngx-bootstrap": "^1.9.3",
"ngx-clipboard": "^8.1.0",
"ngx-loading": "^1.0.14",
"ngx-pagination": "^3.0.0",
"ngx-toastr": "^6.4.0",
"rxjs": "^5.5.6",
"zone.js": "^0.8.19"
},
"devDependencies": {
"@angular/cli": "~1.7.0",
"@angular/compiler-cli": "^5.2.0",
"@angular/language-service": "^5.2.0",
"@types/jasmine": "~2.8.3",
"@types/jasminewd2": "~2.0.2",
"@types/node": "~6.0.60",
"codelyzer": "^4.0.1",
"jasmine-core": "~2.8.0",
"jasmine-spec-reporter": "~4.2.1",
"karma": "~2.0.0",
"karma-chrome-launcher": "~2.2.0",
"karma-coverage-istanbul-reporter": "^1.2.1",
"karma-jasmine": "~1.1.0",
"karma-jasmine-html-reporter": "^0.2.2",
"protractor": "~5.1.2",
"ts-node": "~4.1.0",
"tslint": "~5.9.1",
"typescript": "~2.5.3"
}
}


Everything is fine so far. Now I need to use a datepicker in my app. So I installed angular-io-datepicker

npm install angular-io-datepicker --save


Now, when I do a ng serve (after including the OverlayModule and DatePickerModule in app.module.ts ), it gives me the below error

ERROR in node_modules/@angular/core/src/render3/ng_dev_mode.d.ts(9,11): error TS2451: Cannot redeclare block-scoped variable 'ngDevMode'.
node_modules/angular-io-overlay/node_modules/@angular/core/src/render3/ng_dev_mode.d.ts(9,11): error TS2451: Cannot redeclare block-scoped variable 'ngDevMode'.


Any suggestions on what could be wrong and how to fix it? I was earlier using this module successfully with Angular 4. Then I upgraded to Angular 5 and it broke. Now even if I rollback to angular 4, this module still gives me the same problem.

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