diff --git a/pom.xml b/pom.xml
index a62ca9a..7c76467 100644
--- a/pom.xml
+++ b/pom.xml
@@ -51,7 +51,7 @@
     <properties>
         <gridsuite-dependencies.version>28</gridsuite-dependencies.version>
         <commons-lang3.version>3.9</commons-lang3.version>
-        <powsybl-open-reac.version>0.3.0</powsybl-open-reac.version>
+        <powsybl-open-reac.version>0.4.0</powsybl-open-reac.version>
         <mockito-inline.version>3.11.1</mockito-inline.version>
         <assertj.version>3.24.2</assertj.version>
         <liquibase-hibernate-package>org.gridsuite.voltageinit.server</liquibase-hibernate-package>
diff --git a/src/main/java/org/gridsuite/voltageinit/server/service/VoltageInitService.java b/src/main/java/org/gridsuite/voltageinit/server/service/VoltageInitService.java
index 0766675..4315c7a 100644
--- a/src/main/java/org/gridsuite/voltageinit/server/service/VoltageInitService.java
+++ b/src/main/java/org/gridsuite/voltageinit/server/service/VoltageInitService.java
@@ -16,6 +16,7 @@
 import com.powsybl.openreac.parameters.input.VoltageLimitOverride;
 import com.powsybl.openreac.parameters.input.VoltageLimitOverride.VoltageLimitType;
 
+import com.powsybl.openreac.parameters.input.algo.ReactiveSlackBusesMode;
 import org.gridsuite.voltageinit.server.dto.ReactiveSlack;
 import org.gridsuite.voltageinit.server.dto.VoltageInitResult;
 import org.gridsuite.voltageinit.server.dto.VoltageInitStatus;
@@ -178,6 +179,9 @@ public OpenReacParameters buildOpenReacParameters(Optional<VoltageInitParameters
                 .addVariableTwoWindingsTransformers(variableTwoWindingsTransformers)
                 .addVariableShuntCompensators(variableShuntCompensators);
 
+        //The optimizer will attach reactive slack variables to all buses
+        parameters.setReactiveSlackBusesMode(ReactiveSlackBusesMode.ALL);
+
         long nanoTime = System.nanoTime();
         LOGGER.info("Parameters built in {}s", TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - startTime.getAndSet(nanoTime)));
         return parameters;