diff --git a/include/mbedtls/debug.h b/include/mbedtls/debug.h
index 01d2901..d6dd152 100644
--- a/include/mbedtls/debug.h
+++ b/include/mbedtls/debug.h
@@ -280,7 +280,10 @@
                              const char *text, const mbedtls_x509_crt *crt);
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_OR_ECDHE_ANY_ENABLED)
+/* Note: the MBEDTLS_ECDH_C guard here is mandatory because this debug function
+         only works for the built-in implementation. */
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_OR_ECDHE_ANY_ENABLED) && \
+    defined(MBEDTLS_ECDH_C)
 typedef enum {
     MBEDTLS_DEBUG_ECDH_Q,
     MBEDTLS_DEBUG_ECDH_QP,
@@ -307,7 +310,8 @@
                                const char *file, int line,
                                const mbedtls_ecdh_context *ecdh,
                                mbedtls_debug_ecdh_attr attr);
-#endif
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_ECDH_OR_ECDHE_ANY_ENABLED &&
+          MBEDTLS_ECDH_C */
 
 #ifdef __cplusplus
 }