diff --git a/src/gui/jmem.cpp b/src/gui/jmem.cpp
index cb412db5b..877d53f99 100644
--- a/src/gui/jmem.cpp
+++ b/src/gui/jmem.cpp
@@ -204,9 +204,9 @@ static void addslot(void *ptr, unsigned long size)
 
   p->ptr = ptr;
   p->size = size;
-  p->next = headslot;
 
   ScopedLock lock(*mutex);
+  p->next = headslot;
   headslot = p;
 }