1 files changed, 11 insertions, 3 deletions

diff --git a/src/arena.c b/src/arena.c
index bd93eeb..d02694d 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -23,6 +23,12 @@ chunk_size (struct arena__chunk *chunk)
   return chunk->end - chunk->data;
 }
 
+static size_t
+chunk_used (struct arena__chunk *chunk)
+{
+  return chunk->free - chunk->data;
+}
+
 static struct arena__chunk *
 new_chunk (size_t size)
 {
@@ -206,11 +212,13 @@ arena__coalesce_from_fast (ARENA arena, struct arena__checkpoint checkpoint,
 
   // copy old chunks into new chunk
   size_t other_size = checkpoint.tail->free - checkpoint.free;
-  memcpy (chunk->free, checkpoint.free, other_size);
-  chunk->free += other_size;
+  if (other_size) {
+    memcpy (chunk->free, checkpoint.free, other_size);
+    chunk->free += other_size;
+  }
   for (struct arena__chunk *other_chunk = checkpoint.tail->next;
        other_chunk; other_chunk = other_chunk->next) {
-    other_size = chunk_size (other_chunk);
+    other_size = chunk_used (other_chunk);
     memcpy (chunk->free, other_chunk->data, other_size);
     chunk->free += other_size;
   }