diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index cf1967585..a96516e8e 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -4499,7 +4499,7 @@ const char *Mle::RoleToString(DeviceRole aRole)
     static_assert(kRoleRouter == 3, "kRoleRouter value is incorrect");
     static_assert(kRoleLeader == 4, "kRoleLeader value is incorrect");
 
-    return (aRole <= OT_ARRAY_LENGTH(kRoleStrings)) ? kRoleStrings[aRole] : "invalid";
+    return (aRole < OT_ARRAY_LENGTH(kRoleStrings)) ? kRoleStrings[aRole] : "invalid";
 }
 
 // LCOV_EXCL_START