diff --git a/src/interpreter/heap.c b/src/interpreter/heap.c
index 5408d9d1..d3ea672b 100644
--- a/src/interpreter/heap.c
+++ b/src/interpreter/heap.c
@@ -40,12 +40,12 @@ static void ManagedHeap__fire_debug_callback(ManagedHeap* self, ManagedHeapSwpet
     c11_sbuf buf;
     c11_sbuf__ctor(&buf);
 
-    const int64_t NANOS_PER_SEC = 1000000000;
+    const int64_t NANOS_PER_MS = 1000000000 / 1000;
     const char* DIVIDER = "------------------------------------------------------------\n";
 
     double start = out_info->start_ns / 1e9;
-    int64_t mark_ms = (out_info->mark_end_ns - out_info->start_ns) / NANOS_PER_SEC;
-    int64_t swpet_ms = (out_info->swpet_end_ns - out_info->mark_end_ns) / NANOS_PER_SEC;
+    int64_t mark_ms = (out_info->mark_end_ns - out_info->start_ns) / NANOS_PER_MS;
+    int64_t swpet_ms = (out_info->swpet_end_ns - out_info->mark_end_ns) / NANOS_PER_MS;
 
     c11_sbuf__write_cstr(&buf, DIVIDER);
     pk_sprintf(&buf, "start:        %f\n", (double)start / 1000);