diff --git a/pid/util.cpp b/pid/util.cpp
index 5c6e5d4..0a8f892 100644
--- a/pid/util.cpp
+++ b/pid/util.cpp
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "util.hpp"
+
 #include "ec/pid.hpp"
 
 #include <cstring>