B diffuses in crystalline Si by reacting with a Si self-interstitial (I) with a frequency g and so forming a fast migrating B I complex that can migrate for an average length λ. We experimentally demonstrate that both g and λ strongly depend on the free hole concentration p. At low p, g has a constant trend and λ increases with p, while at high p, g has a superlinear trend and λ decreases with p. This demonstrates that B I forms in the two regimes by interaction with neutral and double positive I, respectively, and its charge state has to change by interaction with free holes before diffusing.