diff --git a/arch/arm/src/mps/mps_allocateheap.c b/arch/arm/src/mps/mps_allocateheap.c
index 186c808aca..78a0d34fe3 100644
--- a/arch/arm/src/mps/mps_allocateheap.c
+++ b/arch/arm/src/mps/mps_allocateheap.c
@@ -174,7 +174,7 @@ void up_allocate_heap(void **heap_start, size_t *heap_size)
   /* Return the heap settings */
 
   *heap_start = (void *)g_idle_topstack;
-  *heap_size  = PRIMARY_RAM_END - g_idle_topstack;
+  *heap_size  = MPS_SRAM1_START + MPS_SRAM1_SIZE - g_idle_topstack;
 #endif
 }