diff --git a/libs/ardour/globals.cc b/libs/ardour/globals.cc
index 3344c61a9a..e83a8ab2e4 100644
--- a/libs/ardour/globals.cc
+++ b/libs/ardour/globals.cc
@@ -224,7 +224,7 @@ setup_hardware_optimization (bool try_optimization)
 				 "movq %%rdx, %0\n"
 		 	     : "=m" (use_sse)
 	   		     : 
- 	    		 : "%rax", "%rcx", "%rdx", "memory");
+ 	    		 : "%rax", "%rbx", "%rcx", "%rdx", "memory");
 
 #endif /* USE_X86_64_ASM */