diff --git a/ulib/dlmalloc/dlmalloc_port.inc b/ulib/dlmalloc/dlmalloc_port.inc
index 9795d71..8ada055 100644
--- a/ulib/dlmalloc/dlmalloc_port.inc
+++ b/ulib/dlmalloc/dlmalloc_port.inc
@@ -54,14 +54,51 @@ static MLOCK_T malloc_global_mutex = { 0 };
 
 #define PAGE_SIZE 0x1000
 
-static uint8_t *heap_start = (uint8_t *)NULL;
+static uint8_t *heap_start = NULL;
 static uint8_t *heap_end = NULL;
+static uint8_t *heap_commit = NULL;
 
 static size_t _roundpage(size_t sz) {
   return (sz + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
 }
 
 void *sbrk(ptrdiff_t inc) {
+  if (!heap_end) {
+    size_t allocsz = PAGE_SIZE;
+    uint8_t *maddr = NULL;
+    int32_t ret = mman_map(NULL, allocsz, MMAN_MAP_PF_RW, 0, &maddr);
+    if (ret != E_OK || maddr == NULL) {
+      return (void *)-1;
+    }
+    heap_start = maddr;
+    heap_end = maddr;
+    heap_commit = maddr + allocsz;
+  }
+
+  if (inc == 0) {
+    return heap_end;
+  }
+
+  uint8_t *oldh = heap_end;
+  uint8_t *newh = heap_end + inc;
+
+  if (inc > 0) {
+    if (newh > heap_commit) {
+      size_t extra = _roundpage((size_t)(newh - heap_commit));
+      uint8_t *maddr = NULL;
+      int32_t ret = mman_map(NULL, extra, MMAN_MAP_PF_RW, 0, &maddr);
+      if (ret != E_OK || maddr == NULL) {
+        return (void *)-1;
+      }
+      heap_commit += extra;
+    }
+    heap_end = newh;
+  } else {
+    heap_end = newh;
+  }
+  return oldh;
+
+  #if 0
   if (!heap_end) {
     heap_end = heap_start;
   }
@@ -89,4 +126,5 @@ void *sbrk(ptrdiff_t inc) {
     heap_end = newh;
   }
   return oldh;
+  #endif
 }