diff --git a/src/core/config/openthread-core-default-config.h b/src/core/config/openthread-core-default-config.h
index d8b1a2e42..a2076b354 100644
--- a/src/core/config/openthread-core-default-config.h
+++ b/src/core/config/openthread-core-default-config.h
@@ -279,8 +279,12 @@
  *
  */
 #ifndef OPENTHREAD_CONFIG_HEAP_INTERNAL_SIZE_NO_DTLS
+#if OPENTHREAD_CONFIG_ECDSA_ENABLE
+#define OPENTHREAD_CONFIG_HEAP_INTERNAL_SIZE_NO_DTLS 2600
+#else
 #define OPENTHREAD_CONFIG_HEAP_INTERNAL_SIZE_NO_DTLS 384
 #endif
+#endif
 
 /**
  * @def OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE