diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 1be1092c7204..9baba9576e99 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -686,12 +686,20 @@ static int __init get_freq(char *name, int cells, unsigned long *val)
 static void start_cpu_decrementer(void)
 {
 #if defined(CONFIG_BOOKE) || defined(CONFIG_40x)
+	unsigned int tcr;
+
 	/* Clear any pending timer interrupts */
 	mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);
 
-	/* Enable decrementer interrupt */
-	mtspr(SPRN_TCR, TCR_DIE);
-#endif /* defined(CONFIG_BOOKE) || defined(CONFIG_40x) */
+	tcr = mfspr(SPRN_TCR);
+	/*
+	 * The watchdog may have already been enabled by u-boot. So leave
+	 * TRC[WP] (Watchdog Period) alone.
+	 */
+	tcr &= TCR_WP_MASK;	/* Clear all bits except for TCR[WP] */
+	tcr |= TCR_DIE;		/* Enable decrementer */
+	mtspr(SPRN_TCR, tcr);
+#endif
 }
 
 void __init generic_calibrate_decr(void)