diff --git a/arch/arm/src/mps/mps_allocateheap.c b/arch/arm/src/mps/mps_allocateheap.c
index 78a0d34fe3e..ab838df831d 100644
--- a/arch/arm/src/mps/mps_allocateheap.c
+++ b/arch/arm/src/mps/mps_allocateheap.c
@@ -174,7 +174,19 @@ void up_allocate_heap(void **heap_start, size_t *heap_size)
   /* Return the heap settings */
 
   *heap_start = (void *)g_idle_topstack;
-  *heap_size  = MPS_SRAM1_START + MPS_SRAM1_SIZE - g_idle_topstack;
+  if (g_idle_topstack > MPS_SRAM1_START + MPS_SRAM1_SIZE)
+    {
+      /* If the range of SRAM1 is exceeded, we think that the extern REGION
+       * is enabled
+       */
+
+      *heap_size  = PRIMARY_RAM_END - g_idle_topstack;
+    }
+  else
+    {
+      *heap_size  = MPS_SRAM1_START + MPS_SRAM1_SIZE - g_idle_topstack;
+    }
+
 #endif
 }