diff --git a/test/unit/core/operation/mechanical_forces_op_test.h b/test/unit/core/operation/mechanical_forces_op_test.h
index 55b4efa14..45a60911c 100644
--- a/test/unit/core/operation/mechanical_forces_op_test.h
+++ b/test/unit/core/operation/mechanical_forces_op_test.h
@@ -17,6 +17,7 @@
 
 #include "core/agent/cell.h"
 #include "core/operation/mechanical_forces_op.h"
+#include "core/operation/operation_registry.h"
 #include "unit/test_util/test_util.h"
 
 namespace bdm {