diff --git a/configure.ac b/configure.ac
index 1f9c6f747..9f6f45407 100644
--- a/configure.ac
+++ b/configure.ac
@@ -87,7 +87,7 @@ GR_PWIN32
 ACX_PTHREAD
 if test x"$acx_pthread_ok" = xyes; then
 	CFLAGS="${CFLAGS} ${PTHREAD_CFLAGS}"
-	CXXFLAGS="${CFLAGS} ${PTHREAD_CFLAGS}"
+	CXXFLAGS="${CXXFLAGS} ${PTHREAD_CFLAGS}"
 fi
 
 AC_SYS_POSIX_TERMIOS()