diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -221,6 +221,10 @@
 
 if test "x$enable_debug" = xyes; then
     CPPFLAGS="$CPPFLAGS -DDEBUG -DDEBUG_LOCKORDER"
+    # Clear default -g -O2 flags
+    if test "x$CXXFLAGS_overridden" = xno; then
+        CXXFLAGS=""
+    fi
     if test "x$GCC" = xyes; then
         CFLAGS="$CFLAGS -g3 -O0"
     fi