diff --git a/configure.ac b/configure.ac
index 65926453b..494877381 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,6 +32,7 @@ LT_INIT
 
 # Checks for programs.
 AC_PROG_CC
+AC_PROG_CC_C99
 
 CFLAGS="-Wall $CFLAGS"