1 files changed, 2 insertions, 2 deletions

diff --git a/config.m4 b/config.m4
index a6dade9..dddea2a 100644
--- a/config.m4
+++ b/config.m4
@@ -29,7 +29,7 @@ fi
 
 AC_MSG_CHECKING([for C11 support with -std=c11])
 old_CFLAGS="$CFLAGS"
-CFLAGS+=" -std=c11"
+CFLAGS="${CFLAGS} -std=c11"
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],[])],[AC_MSG_RESULT([yes])],[
         AC_MSG_RESULT([no])
         CFLAGS="$old_CFLAGS"
@@ -38,7 +38,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],[])],[AC_MSG_RESULT([yes])],[
         echo "  support. Trying C99 instead, but compiling may fail."
         echo "=========================================================="
         AC_MSG_CHECKING([for C99 support with -std=c99])
-        CFLAGS+=" -std=c99"
+        CFLAGS="${CFLAGS} -std=c99"
         AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],[])],[AC_MSG_RESULT([yes])],[
                 AC_MSG_RESULT([no])
                 CFLAGS="$old_CFLAGS"