diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 34e3082632d8311575e27c6d2a4b87c9985dd574..b237e649cd5de2ebe8ed73f96b5507524b8faf6a 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -70,7 +70,7 @@ static unsigned long io_tlb_nslabs;
  */
 static unsigned long io_tlb_overflow = 32*1024;
 
-void *io_tlb_overflow_buffer;
+static void *io_tlb_overflow_buffer;
 
 /*
  * This is a free list describing the number of free entries available from