diff --git a/lib/curl_setup_once.h b/lib/curl_setup_once.h
index d00142fac2..0f5c771f63 100644
--- a/lib/curl_setup_once.h
+++ b/lib/curl_setup_once.h
@@ -273,7 +273,12 @@ typedef unsigned int curl_bit;
  */
 #undef DEBUGASSERT
 #ifdef DEBUGBUILD
+#ifdef CURL_DEBUGASSERT
+/* External assertion handler for custom integrations */
+#define DEBUGASSERT(x) CURL_DEBUGASSERT(x)
+#else
 #define DEBUGASSERT(x) assert(x)
+#endif
 #else
 #define DEBUGASSERT(x) do {} while(0)
 #endif