diff --git a/libecole/include/ecole/dynamics/primalsearch.hpp b/libecole/include/ecole/dynamics/primalsearch.hpp
index b45cf8e5d..b3865c2f4 100644
--- a/libecole/include/ecole/dynamics/primalsearch.hpp
+++ b/libecole/include/ecole/dynamics/primalsearch.hpp
@@ -37,7 +37,7 @@ class PrimalSearchDynamics : public EnvironmentDynamics<VarIdsVals, std::optiona
 	int depth_start;
 	int depth_stop;
 
-	int trials_spent = 0;                 // to keep track of the number of trials during each search
+	unsigned int trials_spent = 0;                 // to keep track of the number of trials during each search
 	SCIP_HEUR* heur = nullptr;            // to tell SCIP where primal solutions come from
 	SCIP_RESULT result = SCIP_DIDNOTRUN;  // the final result of each search (several trials)
 };