diff --git a/simgear/structure/SGAtomic.cxx b/simgear/structure/SGAtomic.cxx
index a31478f5..e7dd76c2 100644
--- a/simgear/structure/SGAtomic.cxx
+++ b/simgear/structure/SGAtomic.cxx
@@ -20,7 +20,7 @@
 
 #include "SGAtomic.hxx"
 
-#if !defined(SGATOMIC_USE_GCC4_BUILTINS) && defined (__i386__)
+#if defined(SGATOMIC_USE_GCC4_BUILTINS) && defined (__i386__)
 
 // Usually the apropriate functions are inlined by gcc.
 // But if gcc is called with something aequivalent to -march=i386,