diff --git a/src/core/meshcop/dtls.cpp b/src/core/meshcop/dtls.cpp
index 97afbc826..6f71ea766 100644
--- a/src/core/meshcop/dtls.cpp
+++ b/src/core/meshcop/dtls.cpp
@@ -516,6 +516,7 @@ otError Dtls::MapError(int rval)
         break;
 
     case MBEDTLS_ERR_SSL_ALLOC_FAILED:
+    case MBEDTLS_ERR_SSL_WANT_WRITE:
         error = OT_ERROR_NO_BUFS;
         break;
 
diff --git a/src/core/openthread-core-default-config.h b/src/core/openthread-core-default-config.h
index 4f40aa62b..001fbecc7 100644
--- a/src/core/openthread-core-default-config.h
+++ b/src/core/openthread-core-default-config.h
@@ -92,7 +92,7 @@
  *
  */
 #ifndef OPENTHREAD_CONFIG_NUM_MESSAGE_BUFFERS
-#define OPENTHREAD_CONFIG_NUM_MESSAGE_BUFFERS 40
+#define OPENTHREAD_CONFIG_NUM_MESSAGE_BUFFERS 44
 #endif
 
 /**