diff --git a/lib/stm32/f0/rcc.c b/lib/stm32/f0/rcc.c
index 8f964639..69bdbd88 100644
--- a/lib/stm32/f0/rcc.c
+++ b/lib/stm32/f0/rcc.c
@@ -250,7 +250,7 @@ void rcc_osc_on(enum rcc_osc osc)
 		RCC_CSR |= RCC_CSR_LSION;
 		break;
 	case PLL:
-		/* don't do anything */
+		RCC_CR|=RCC_CR_PLLON; 
 		break;
 	}
 }