diff --git a/hardware_interface/test/test_macros.cpp b/hardware_interface/test/test_macros.cpp
index 18e9e292c0..c32497c6b1 100644
--- a/hardware_interface/test/test_macros.cpp
+++ b/hardware_interface/test/test_macros.cpp
@@ -62,7 +62,7 @@ TEST_F(TestMacros, throw_on_not_null)
   EXPECT_ANY_THROW(THROW_ON_NOT_NULLPTR(a_ptr));
 
   std::vector<int *> vec_ptr;
-  for (auto i : {0, 1, 2})
+  for (size_t i : {0, 1, 2})
   {
     vec_ptr.push_back(i_ptr);
     EXPECT_ANY_THROW(THROW_ON_NOT_NULLPTR(vec_ptr[i]));