diff --git a/configure.ac b/configure.ac
index 7ca2145..0413332 100644
--- a/configure.ac
+++ b/configure.ac
@@ -253,7 +253,10 @@ 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