diff --git a/lib/stm32/l1/rcc.c b/lib/stm32/l1/rcc.c
index 0bf0fa35..7a7d8ccb 100644
--- a/lib/stm32/l1/rcc.c
+++ b/lib/stm32/l1/rcc.c
@@ -498,9 +498,14 @@ void rcc_clock_setup_hsi(const clock_scale_t *clock)
 
 void rcc_clock_setup_pll(const clock_scale_t *clock)
 {
-	/* Enable internal high-speed oscillator. */
-	rcc_osc_on(HSI);
-	rcc_wait_for_osc_ready(HSI);
+	/* Turn on the appropriate source for the PLL */
+	if (clock->pll_source == RCC_CFGR_PLLSRC_HSE_CLK) {
+		rcc_osc_on(HSE);
+		rcc_wait_for_osc_ready(HSE);
+	} else {
+		rcc_osc_on(HSI);
+		rcc_wait_for_osc_ready(HSI);
+	}
 
 	/*
 	 * Set prescalers for AHB, ADC, ABP1, ABP2.