Mobile apps are ubiquitous in our lives as they provide numerous services to support our daily activities. Personalizing such services entail collecting (possibly sensitive) personal information. Mobile apps must therefore comply with privacy regulations like the General Data Protection Regulation (GDPR) enforced in the European Union (EU). To achieve compliance, an app should implement the legal requirements pertinent to data collection and processing according to the GDPR. Privacy policies associated with apps can serve as intermediary instruments connecting between source code and regulations. They explain to app users how activities involving personal data are implemented and provide a detailed view on how legal requirements are operationalized in the app. Incomplete policies can indicate non-compliant apps. This paper sheds light on the state-of-practice of GDPR compliance in two mainstream app markets: the Apple App Store and the Google Play Store. We conducted a study to assess the completeness of 470 apps privacy policies in these stores according to the GDPR. Our analysis shows that, irrespective of the app store, fundamental GDPR requirements (e.g., information pertinent to individuals’ rights and details of data transfer outside EU) are missing in ≈92% of the analyzed policies, revealing potential breaches in the respective apps.