diff --git a/xpcom/reflect/xptcall/src/md/unix/xptc_platforms_unixish_x86.h b/xpcom/reflect/xptcall/src/md/unix/xptc_platforms_unixish_x86.h
index ac4022f2772..c9b2a730467 100644
--- a/xpcom/reflect/xptcall/src/md/unix/xptc_platforms_unixish_x86.h
+++ b/xpcom/reflect/xptcall/src/md/unix/xptc_platforms_unixish_x86.h
@@ -72,7 +72,13 @@
 #define THUNK_BASED_THIS_ADJUST
 
 #elif defined(__OpenBSD__) 
+/* OpenBSD instroduces GCC 2.95.x in late May 1999 */
+#include <sys/param.h>
+#if OpenBSD <= 199905
 #define THUNK_BASED_THIS_ADJUST
+#else
+#define CFRONT_STYLE_THIS_ADJUST
+#endif
 
 #elif defined(__bsdi__) 
 #include <sys/param.h>