diff --git a/arch/arm/src/lpc43xx/lpc43_cgu.c b/arch/arm/src/lpc43xx/lpc43_cgu.c
index 036da2697c..180d17bda6 100644
--- a/arch/arm/src/lpc43xx/lpc43_cgu.c
+++ b/arch/arm/src/lpc43xx/lpc43_cgu.c
@@ -151,9 +151,9 @@ static inline void lpc43_xtalconfig(void)
 #endif
   putreg32(regval, LPC43_XTAL_OSC_CTRL);
 
-  /* Enable the crystal oscillator */
+  /* Enable the crystal oscillator by taking it out of power down mode */
 
-  regval |= XTAL_OSC_CTRL_ENABLE;
+  regval &= ~XTAL_OSC_CTRL_ENABLE;
   putreg32(regval, LPC43_XTAL_OSC_CTRL);
 
   /* Delay for stable clock input */