diff --git a/src/ikarus-collect.c b/src/ikarus-collect.c
index e1701ba..519bf67 100644
--- a/src/ikarus-collect.c
+++ b/src/ikarus-collect.c
@@ -505,12 +505,11 @@ ik_collect(int mem_req, ikpcb* pcb){
   int free_space = 
     ((unsigned int)pcb->allocation_redline) - 
     ((unsigned int)pcb->allocation_pointer);
-  #define HEAPSIZE (1024 * 4096)
-  if((free_space <= mem_req) || (pcb->heap_size < HEAPSIZE)){
+  if((free_space <= mem_req) || (pcb->heap_size < IK_HEAPSIZE)){
 #ifndef NDEBUG
     fprintf(stderr, "REQ=%d, got %d\n", mem_req, free_space);
 #endif
-    int memsize = (mem_req>HEAPSIZE) ? mem_req : HEAPSIZE;
+    int memsize = (mem_req > IK_HEAPSIZE) ? mem_req : IK_HEAPSIZE;
     memsize = align_to_next_page(memsize);
     ik_munmap_from_segment(
         pcb->heap_base,
diff --git a/src/ikarus-data.h b/src/ikarus-data.h
index ac1f03c..f3c0863 100644
--- a/src/ikarus-data.h
+++ b/src/ikarus-data.h
@@ -294,6 +294,7 @@ ikp ik_safe_alloc(ikpcb* pcb, int size);
 #define IK_OFF_CAR    (IK_DISP_CAR - IK_PAIR_TAG)
 #define IK_OFF_CDR    (IK_DISP_CDR - IK_PAIR_TAG)
 #define IK_HEAP_EXT_SIZE  (32 * 4096)
+#define IK_HEAPSIZE (1024 * 4096) /* 4 MB */
 #define IK_PAIRP(x)   (IK_PTAG(x) == IK_PAIR_TAG)
 #define IK_CHARP(x)   (IK_MASK(x,IK_CHAR_MASK) == IK_CHAR_TAG)
 #define IK_STRING_TAG     6
diff --git a/src/ikarus-process.c b/src/ikarus-process.c
index b53356a..7c4926f 100644
--- a/src/ikarus-process.c
+++ b/src/ikarus-process.c
@@ -2,6 +2,7 @@
 #include <sys/types.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 #include "ikarus-data.h"
 #include <errno.h>
 
diff --git a/src/ikarus-runtime.c b/src/ikarus-runtime.c
index 52c37c2..ac81991 100644
--- a/src/ikarus-runtime.c
+++ b/src/ikarus-runtime.c
@@ -279,13 +279,12 @@ ikpcb* ik_make_pcb(){
   ikpcb* pcb = ik_malloc(sizeof(ikpcb));
   bzero(pcb, sizeof(ikpcb));
   pcb->collect_key = false_object;
-  #define HEAPSIZE (1024 * 4096)
   #define STAKSIZE (1024 * 4096)
   //#define STAKSIZE (256 * 4096)
-  pcb->heap_base = ik_mmap(HEAPSIZE);
-  pcb->heap_size = HEAPSIZE;
+  pcb->heap_base = ik_mmap(IK_HEAPSIZE);
+  pcb->heap_size = IK_HEAPSIZE;
   pcb->allocation_pointer = pcb->heap_base;
-  pcb->allocation_redline = pcb->heap_base + HEAPSIZE - 2 * 4096;
+  pcb->allocation_redline = pcb->heap_base + IK_HEAPSIZE - 2 * 4096;
 
   pcb->stack_base = ik_mmap(STAKSIZE);
   pcb->stack_size = STAKSIZE;