diff --git a/src/core/coap/coap_message.cpp b/src/core/coap/coap_message.cpp
index 23d9cbd52..22c846c77 100644
--- a/src/core/coap/coap_message.cpp
+++ b/src/core/coap/coap_message.cpp
@@ -200,7 +200,7 @@ otError Message::AppendUintOption(uint16_t aNumber, uint32_t aValue)
 
     Encoding::BigEndian::WriteUint32(aValue, buffer);
 
-    while (value[0] == 0 && length > 0)
+    while ((length > 0) && (value[0] == 0))
     {
         value++;
         length--;