diff --git a/arch/sim/src/up_allocateheap.c b/arch/sim/src/up_allocateheap.c
index 9278faf2725..f02f8cbfa0a 100644
--- a/arch/sim/src/up_allocateheap.c
+++ b/arch/sim/src/up_allocateheap.c
@@ -81,5 +81,5 @@ static uint8_t sim_heap[SIM_HEAP_SIZE];
 void up_allocate_heap(void **heap_start, size_t *heap_size)
 {
   *heap_start = sim_heap;
-  *heap_size = SIM_HEAP_SIZE;
+  *heap_size  = SIM_HEAP_SIZE;
 }
diff --git a/arch/sim/src/up_internal.h b/arch/sim/src/up_internal.h
index 7f241e48e3c..094776390fa 100644
--- a/arch/sim/src/up_internal.h
+++ b/arch/sim/src/up_internal.h
@@ -40,6 +40,7 @@
  * Included Files
  **************************************************************************/
 
+#include <nuttx/config.h>
 #include <sys/types.h>
 #include <nuttx/irq.h>
 
@@ -64,7 +65,13 @@
 # define JB_PC  (5)
 #endif /* __ASSEMBLY__ */
 
-#define SIM_HEAP_SIZE (4*1024*1024)
+/* Size of the simulated heap */
+
+#if CONFIG_MM_SMALL
+#  define SIM_HEAP_SIZE (64*1024)
+#else
+#  define SIM_HEAP_SIZE (4*1024*1024)
+#endif
 
 /* These definitions characterize the compressed filesystem image */