diff --git a/cpu/cc2538/startup-gcc.c b/cpu/cc2538/startup-gcc.c
index 231b83f18..e09356e4d 100644
--- a/cpu/cc2538/startup-gcc.c
+++ b/cpu/cc2538/startup-gcc.c
@@ -103,7 +103,7 @@ void uart1_isr(void);
 #endif
 /*---------------------------------------------------------------------------*/
 /* Allocate stack space */
-static unsigned long stack[512] __attribute__ ((section(".stack")));
+static uint64_t stack[256] __attribute__ ((section(".stack")));
 /*---------------------------------------------------------------------------*/
 __attribute__((__section__(".vectors")))
 void(*const vectors[])(void) =