diff --git a/arch/s390/hypfs/hypfs_vm.c b/arch/s390/hypfs/hypfs_vm.c
index 32040ace00ea..afbe07907c10 100644
--- a/arch/s390/hypfs/hypfs_vm.c
+++ b/arch/s390/hypfs/hypfs_vm.c
@@ -231,7 +231,7 @@ failed:
 struct dbfs_d2fc_hdr {
 	u64	len;		/* Length of d2fc buffer without header */
 	u16	version;	/* Version of header */
-	char	tod_ext[16];	/* TOD clock for d2fc */
+	char	tod_ext[STORE_CLOCK_EXT_SIZE]; /* TOD clock for d2fc */
 	u64	count;		/* Number of VM guests in d2fc buffer */
 	char	reserved[30];
 } __attribute__ ((packed));
diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 8beee1cceba4..98eb2a579223 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -67,20 +67,22 @@ static inline void local_tick_enable(unsigned long long comp)
 	set_clock_comparator(S390_lowcore.clock_comparator);
 }
 
-#define CLOCK_TICK_RATE	1193180 /* Underlying HZ */
+#define CLOCK_TICK_RATE		1193180 /* Underlying HZ */
+#define STORE_CLOCK_EXT_SIZE	16	/* stcke writes 16 bytes */
 
 typedef unsigned long long cycles_t;
 
-static inline void get_tod_clock_ext(char clk[16])
+static inline void get_tod_clock_ext(char *clk)
 {
-	typedef struct { char _[sizeof(clk)]; } addrtype;
+	typedef struct { char _[STORE_CLOCK_EXT_SIZE]; } addrtype;
 
 	asm volatile("stcke %0" : "=Q" (*(addrtype *) clk) : : "cc");
 }
 
 static inline unsigned long long get_tod_clock(void)
 {
-	unsigned char clk[16];
+	unsigned char clk[STORE_CLOCK_EXT_SIZE];
+
 	get_tod_clock_ext(clk);
 	return *((unsigned long long *)&clk[1]);
 }