diff --git a/gcc/config/i386/xm-aix.h b/gcc/config/i386/xm-aix.h
index e3e673972c3..d434a53e923 100644
--- a/gcc/config/i386/xm-aix.h
+++ b/gcc/config/i386/xm-aix.h
@@ -49,6 +49,10 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 #define bzero(a,b) memset (a,0,b)
 #define bcmp(a,b,c) memcmp (a,b,c)
 
+/* If compiled with GNU C, use the built-in alloca.  */
+#undef alloca
 #ifdef __GNUC__
-#define alloca(n) __builtin_alloca(n)
+#define alloca __builtin_alloca
+#else
+#define USE_C_ALLOCA
 #endif
diff --git a/gcc/config/i386/xm-sysv4.h b/gcc/config/i386/xm-sysv4.h
index 955c42d7741..6aa397c6b32 100644
--- a/gcc/config/i386/xm-sysv4.h
+++ b/gcc/config/i386/xm-sysv4.h
@@ -2,3 +2,11 @@
 
 #include "xm-i386.h"
 #include "xm-svr4.h"
+
+/* If compiled with GNU C, use the built-in alloca.  */
+#undef alloca
+#ifdef __GNUC__
+#define alloca __builtin_alloca
+#else
+#define USE_C_ALLOCA
+#endif