diff --git a/configure.ac b/configure.ac
index 84a4a0b39..88fde482b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -40,6 +40,10 @@ CYASSL_LIBRARY_VERSION=3:3:0
 #               +- increment if interfaces have been added, removed or changed
 AC_SUBST(CYASSL_LIBRARY_VERSION)
 
+# capture user C_EXTRA_FLAGS from ./configure line, CFLAGS may hold -g -O2 even
+# if user doesn't override, no way to tell
+USER_C_EXTRA_FLAGS="$C_EXTRA_FLAGS"
+
 LT_INIT([win32-dll])
 LT_LANG([C++])
 LT_LANG([C])
@@ -700,6 +704,9 @@ fi])
 
 AX_HARDEN_CC_COMPILER_FLAGS
 
+# add user C_EXTRA_FLAGS back
+CFLAGS="$CFLAGS $USER_C_EXTRA_FLAGS"
+
 CREATE_HEX_VERSION
 AC_SUBST([AM_CPPFLAGS])
 AC_SUBST([AM_CFLAGS])
diff --git a/m4/ax_harden_compiler_flags.m4 b/m4/ax_harden_compiler_flags.m4
index 5818cf24b..a32cef3c9 100644
--- a/m4/ax_harden_compiler_flags.m4
+++ b/m4/ax_harden_compiler_flags.m4
@@ -97,6 +97,7 @@
 
       AC_LANG_PUSH([C])
 
+      CFLAGS=
       ac_cv_warnings_as_errors=no
       ax_append_compile_cflags_extra=
       AS_IF([test "$ac_cv_vcs_checkout" = "yes"],[