diff --git a/configure.ac b/configure.ac
index e575a20..81a7772 100644
--- a/configure.ac
+++ b/configure.ac
@@ -228,7 +228,10 @@ dnl **********************************************************************
CURL_CHECK_COMPILER
CURL_SET_COMPILER_BASIC_OPTS
-CURL_SET_COMPILER_DEBUG_OPTS
+
+dnl do not perturb CFLAGS given by the build system
+dnl CURL_SET_COMPILER_DEBUG_OPTS
+
CURL_SET_COMPILER_OPTIMIZE_OPTS
CURL_SET_COMPILER_WARNING_OPTS