diff --git a/src/simulator/uint64x64-cairo.h b/src/simulator/uint64x64-cairo.h
index 6704facd1..e1d4417fa 100644
--- a/src/simulator/uint64x64-cairo.h
+++ b/src/simulator/uint64x64-cairo.h
@@ -6,7 +6,8 @@
 #include "cairo-wideint-private.h"
 
 #ifdef __i386__
-#define UINT64x64_CAIRO_ASM 1
+// this assembly code does not appear to work right yet.
+#define noUINT64x64_CAIRO_ASM 1
 #endif
 
 namespace ns3 {