During the 1960s, as the Sino-Soviet conflict raged on, North Korea, for the first time in its history, officially began to reject the USSR’s ideological leadership and instead tread its own path under the slogan of self-reliance. As a result, those forces aligned with the Soviet Union, especially East Germany, heavily criticized North Korea’s new ideological path. Drawing on the East German archives, this study seeks to understand the nature of fraternal criticisms and their implications for the development of North Korean ideology in the 1960s. Scholars typically stress North Korean ideology’s departure from Marxism-Leninism, sometimes suggesting a departure as early as the 1950s. The present study, based on a thorough reading of archival documents and North Korean materials, challenges such portrayals, arguing that North Korea remained in the Marxist-Leninist tradition even while contesting Soviet orthodoxy. Developments in North Korean ideology were far more gradual than is usually assumed, building on what came before. These developments were by no means revolutionary or removed from the global intellectual environment. The Soviets and East Germans could understand North Korean heterodoxy and engage with it in Marxist-Leninist terms, just as North Korea did with Soviet Marxism-Leninism—there was no fundamental ideological split.