diff --git a/configure.ac b/configure.ac
index 85b7b342..68b649e9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -114,7 +114,7 @@ AS_CASE([$host_os],
 AC_FUNC_MMAP
 
 AC_CHECK_FUNC([strndup], [
-	AC_DEFINE([HAVE_STRNDUP], [], [strndup appears to be present])
+    AC_DEFINE([HAVE_STRNDUP], [], [strndup appears to be present])
 ])
 
 AC_CHECK_HEADER([execinfo.h], [break])