diff --git a/platforms/msdos/extras.c b/platforms/msdos/extras.c
index 8a06be3..ecbf84a 100644
--- a/platforms/msdos/extras.c
+++ b/platforms/msdos/extras.c
@@ -36,15 +36,21 @@ time_t time(time_t *t)
 
 void *malloc(size_t v)
 {
-    static char heap[4096];
+    static char heap[5000];
     static char *heap_ptr = heap;
     char *old_heap_ptr;
 
-    old_heap_ptr = heap_ptr;
-    heap_ptr += v;
+    if (sizeof(heap) - (heap_ptr - heap) < v) {
+        asm __volatile("int $16\n"
+                       "jmp exit"
+                       :
+                       : "a"((uint16_t)0));
 
-    if (heap_ptr > heap + sizeof(heap))
         return NULL;
+    }
+
+    old_heap_ptr = heap_ptr;
+    heap_ptr += v;
 
     return old_heap_ptr;
 }