diff --git a/src/join.c b/src/join.c
index 56819f6c8..d26b25635 100644
--- a/src/join.c
+++ b/src/join.c
@@ -19,6 +19,20 @@
 
 #include <config.h>
 
+#ifdef __GNUC__
+#define alloca __builtin_alloca
+#else /* not __GNUC__ */
+#if HAVE_ALLOCA_H
+#include <alloca.h>
+#else /* not HAVE_ALLOCA_H */
+#ifdef _AIX
+ #pragma alloca
+#else /* not _AIX */
+char *alloca ();
+#endif /* not _AIX */
+#endif /* not HAVE_ALLOCA_H */
+#endif /* not __GNUC__ */
+
 /* Get isblank from GNU libc.  */
 #define _GNU_SOURCE