diff --git a/CMakeLists_files.cmake b/CMakeLists_files.cmake
index bb6eed25a99..16cc5379bdb 100644
--- a/CMakeLists_files.cmake
+++ b/CMakeLists_files.cmake
@@ -284,6 +284,7 @@ if(ENABLE_ECL_INPUT)
     opm/input/eclipse/Schedule/ResCoup/GrupSlav.cpp
     opm/input/eclipse/Schedule/ResCoup/MasterGroup.cpp
     opm/input/eclipse/Schedule/ResCoup/Slaves.cpp
+    opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.cpp
     opm/input/eclipse/Schedule/UDQ/UDQKeywordHandlers.cpp
     opm/input/eclipse/Schedule/UDQ/UDQActive.cpp
     opm/input/eclipse/Schedule/UDQ/UDQAssign.cpp
@@ -1310,6 +1311,7 @@ if(ENABLE_ECL_INPUT)
        opm/input/eclipse/Schedule/ResCoup/GrupSlav.hpp
        opm/input/eclipse/Schedule/ResCoup/MasterGroup.hpp
        opm/input/eclipse/Schedule/ResCoup/Slaves.hpp
+       opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.hpp
        opm/input/eclipse/Schedule/VFPInjTable.hpp
        opm/input/eclipse/Schedule/VFPProdTable.hpp
        opm/input/eclipse/Schedule/Well/Connection.hpp
diff --git a/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.cpp b/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.cpp
new file mode 100644
index 00000000000..7fc4084d497
--- /dev/null
+++ b/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.cpp
@@ -0,0 +1,58 @@
+/*
+  Copyright 2024 Equinor ASA.
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+
+#include <opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.hpp>
+#include <opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.hpp>
+#include <opm/input/eclipse/Schedule/ScheduleState.hpp>
+#include <opm/input/eclipse/Parser/ParserKeywords/R.hpp>
+#include <opm/common/OpmLog/OpmLog.hpp>
+#include <opm/common/utility/OpmInputError.hpp>
+#include "../HandlerContext.hpp"
+
+
+namespace Opm {
+
+void handleRCMASTS(HandlerContext& handlerContext)
+{
+    auto& schedule_state = handlerContext.state();
+    auto rescoup = schedule_state.rescoup();
+    auto tuning = schedule_state.tuning();
+    const auto& keyword = handlerContext.keyword;
+    if (keyword.size() != 1) {
+        throw OpmInputError("RCMASTS keyword requires exactly one record.", keyword.location());
+    }
+    auto record = keyword[0];
+    auto deck_item = record.getItem<ParserKeywords::RCMASTS::MIN_TSTEP>();
+    if (deck_item.defaultApplied(0)) {
+        // The default value is the current value TSMINZ
+        rescoup.masterMinTimeStep(tuning.TSMINZ);
+    }
+    else {
+        auto tstep = deck_item.getSIDouble(0);
+        if (tstep < 0.0) {
+            throw OpmInputError("Negative value for RCMASTS is not allowed.", keyword.location());
+        }
+        rescoup.masterMinTimeStep(tstep);
+    }
+    schedule_state.rescoup.update( std::move( rescoup ));
+}
+
+} // namespace Opm
+
diff --git a/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.hpp b/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.hpp
new file mode 100644
index 00000000000..a963a9fbc45
--- /dev/null
+++ b/opm/input/eclipse/Schedule/ResCoup/MasterMinimumTimeStep.hpp
@@ -0,0 +1,28 @@
+/*
+  Copyright 2024 Equinor ASA.
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef RESERVOIR_COUPLING_MASTER_MINIMUM_TIMESTEP_HPP
+#define RESERVOIR_COUPLING_MASTER_MINIMUM_TIMESTEP_HPP
+namespace Opm {
+
+class HandlerContext;
+
+extern void handleRCMASTS(HandlerContext& handlerContext);
+
+} // namespace Opm
+#endif // RESERVOIR_COUPLING_MASTER_MINIMUM_TIMESTEP_HPP
diff --git a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.cpp b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.cpp
index d71a082db37..3e086af3538 100644
--- a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.cpp
+++ b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.cpp
@@ -27,7 +27,8 @@ namespace ReservoirCoupling {
 bool CouplingInfo::operator==(const CouplingInfo& rhs) const {
     return this->m_slaves == rhs.m_slaves &&
            this->m_master_groups == rhs.m_master_groups &&
-           this->m_grup_slavs == rhs.m_grup_slavs;
+           this->m_grup_slavs == rhs.m_grup_slavs &&
+           this->m_master_min_time_step == rhs.m_master_min_time_step;
 }
 
 CouplingInfo CouplingInfo::serializationTestObject()
diff --git a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.hpp b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.hpp
index 3c319eb59cf..eeef31188be 100644
--- a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.hpp
+++ b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingInfo.hpp
@@ -53,6 +53,7 @@ class CouplingInfo {
     bool hasGrupSlav(const std::string& name) const {
         return m_grup_slavs.find(name) != m_grup_slavs.end();
     }
+
     bool hasMasterGroup(const std::string& name) const {
         return m_master_groups.find(name) != m_master_groups.end();
     }
@@ -69,10 +70,18 @@ class CouplingInfo {
     const MasterGroup& masterGroup(const std::string& name) const {
         return m_master_groups.at(name);
     }
+
     int masterGroupCount() const {
         return m_master_groups.size();
     }
 
+    double masterMinTimeStep() const {
+        return m_master_min_time_step;
+    }
+    void masterMinTimeStep(double tstep) {
+        m_master_min_time_step = tstep;
+    }
+
     const std::map<std::string, Slave>& slaves() const {
         return this->m_slaves;
     }
@@ -93,11 +102,14 @@ class CouplingInfo {
         serializer(m_slaves);
         serializer(m_master_groups);
         serializer(m_grup_slavs);
+        serializer(m_master_min_time_step);
     }
+
 private:
     std::map<std::string, Slave> m_slaves;
     std::map<std::string, MasterGroup> m_master_groups;
     std::map<std::string, GrupSlav> m_grup_slavs;
+    double m_master_min_time_step{0.0};
 };
 
 } // namespace Opm::ReservoirCoupling
diff --git a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingKeywordHandlers.cpp b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingKeywordHandlers.cpp
index 4e7a0082b76..3d2301566cd 100644
--- a/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingKeywordHandlers.cpp
+++ b/opm/input/eclipse/Schedule/ResCoup/ReservoirCouplingKeywordHandlers.cpp
@@ -23,22 +23,20 @@
 #include "GrupSlav.hpp"
 #include "Slaves.hpp"
 #include "MasterGroup.hpp"
+#include "MasterMinimumTimeStep.hpp"
 
 #include <fmt/format.h>
 
 namespace Opm {
 
-namespace {
-
-} // anonymous namespace
-
 std::vector<std::pair<std::string,KeywordHandlers::handler_function>>
 getReservoirCouplingHandlers()
 {
     return {
         { "SLAVES", &handleSLAVES },
         { "GRUPMAST", &handleGRUPMAST},
-        { "GRUPSLAV", &handleGRUPSLAV}
+        { "GRUPSLAV", &handleGRUPSLAV},
+        { "RCMASTS", &handleRCMASTS},
     };
 }
 
diff --git a/tests/parser/ReservoirCouplingTests.cpp b/tests/parser/ReservoirCouplingTests.cpp
index ddf8c710bba..294868e0463 100644
--- a/tests/parser/ReservoirCouplingTests.cpp
+++ b/tests/parser/ReservoirCouplingTests.cpp
@@ -32,6 +32,7 @@
 #include <opm/input/eclipse/EclipseState/Grid/FieldPropsManager.hpp>
 #include <opm/input/eclipse/EclipseState/Tables/TableManager.hpp>
 #include <opm/input/eclipse/Python/Python.hpp>
+#include <opm/input/eclipse/Units/Units.hpp>
 #include <opm/common/utility/OpmInputError.hpp>
 #include <opm/common/OpmLog/OpmLog.hpp>
 #include <opm/common/OpmLog/StreamLog.hpp>
@@ -41,7 +42,7 @@
 
 using namespace Opm;
 namespace {
-Schedule make_schedule(const std::string& schedule_string, bool slave_mode) {
+Schedule makeSchedule(const std::string& schedule_string, bool slave_mode) {
     Parser parser;
     auto python = std::make_shared<Python>();
     Deck deck = parser.parseString(schedule_string);
@@ -61,11 +62,11 @@ void addStringLogger(std::ostringstream& stream_buffer) {
 }
 
 void assertRaisesInputErrorException(const std::string& schedule_string, bool slave_mode, const std::string& exception_string) {
-    BOOST_CHECK_THROW(make_schedule(schedule_string, slave_mode), Opm::OpmInputError);
+    BOOST_CHECK_THROW(makeSchedule(schedule_string, slave_mode), Opm::OpmInputError);
     try {
         // Now that we know that it will throw the specific exception Opm::OpmInputError,
         //  we can check that the exception message is correct
-        make_schedule(schedule_string, slave_mode);
+        makeSchedule(schedule_string, slave_mode);
     }
     catch (const Opm::OpmInputError& e) {
         BOOST_CHECK_EQUAL(std::string(e.what()), exception_string);
@@ -96,51 +97,85 @@ void checkLastLineStringBuffer(
     }
 }
 
+std::string getMinimumMasterTimeStepDeckString(const std::string &end_of_deck_string)
+{
+    std::string prefix = R"(
+SCHEDULE
+
+GRUPTREE
+ 'PLAT-A' 'FIELD' /
+
+ 'MOD1'   'PLAT-A' /
+
+ 'B1_M'   'MOD1' /
+ 'D1_M'   'MOD1' /
+ 'C1_M'   'MOD1' /
+
+ 'E1_M'   'PLAT-A' /
+/
+
+SLAVES
+  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
+  'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
+/
+
+GRUPMAST
+  'D1_M' 'RES-1'  'MANI-D'  1*  /
+  'B1_M' 'RES-1'  'MANI-B'  1*  /
+  'C1_M' 'RES-1'  'MANI-C'  1*  /
+  'E1_M' 'RES-2'  'E1'  1*  /
+/
+)";
+    return prefix + end_of_deck_string;
+}
+
 void removeStringLogger() {
     OpmLog::removeBackend("MYLOGGER");
 }
 
 }  // namespace
 
-// -------------------------------
-// Testing SLAVES keyword
-// -------------------------------
+// ----------------------------------------------
+// Testing SLAVES keyword (sorted alphabetically)
+// ----------------------------------------------
+BOOST_AUTO_TEST_SUITE(SlaveTests)
 
-BOOST_AUTO_TEST_CASE(SLAVES_OK) {
+BOOST_AUTO_TEST_CASE(FAIL_NEGATIVE_NUMPROCS) {
     std::string deck_string = R"(
-
 SCHEDULE
 SLAVES
-  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
+  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  -4 /
   'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
 /
 
 )";
 
-    const auto& schedule = make_schedule(deck_string, /*slave_mode=*/false);
-    const auto& rescoup = schedule[0].rescoup();
-    BOOST_CHECK(rescoup.hasSlave("RES-1"));
-    auto slave = rescoup.slave("RES-1");
-    BOOST_CHECK_EQUAL(slave.name(), "RES-1");
-    BOOST_CHECK_EQUAL(slave.dataFilename(), "RC-01_MOD1_PRED");
-    BOOST_CHECK_EQUAL(slave.directoryPath(), "../mod1");
-    BOOST_CHECK_EQUAL(slave.numprocs(), 4);
+    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/ "Problem with keyword SLAVES\nIn <memory string> line 3\nNumber of processors must be positive. Got: -4.");
 }
 
-BOOST_AUTO_TEST_CASE(SLAVES_FAIL_NEGATIVE_NUMPROCS) {
+BOOST_AUTO_TEST_CASE(SYNTAX_OK) {
     std::string deck_string = R"(
+
 SCHEDULE
 SLAVES
-  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  -4 /
+  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
   'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
 /
 
 )";
 
-    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/ "Problem with keyword SLAVES\nIn <memory string> line 3\nNumber of processors must be positive. Got: -4.");
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
+    const auto& rescoup = schedule[0].rescoup();
+    BOOST_CHECK(rescoup.hasSlave("RES-1"));
+    auto slave = rescoup.slave("RES-1");
+    BOOST_CHECK_EQUAL(slave.name(), "RES-1");
+    BOOST_CHECK_EQUAL(slave.dataFilename(), "RC-01_MOD1_PRED");
+    BOOST_CHECK_EQUAL(slave.directoryPath(), "../mod1");
+    BOOST_CHECK_EQUAL(slave.numprocs(), 4);
 }
 
-BOOST_AUTO_TEST_CASE(SLAVES_WARN_DUPLICATE_NAME) {
+
+BOOST_AUTO_TEST_CASE(WARN_DUPLICATE_NAME) {
     std::string deck_string = R"(
 SCHEDULE
 SLAVES
@@ -151,7 +186,7 @@ SLAVES
 )";
     std::ostringstream stream_buffer;
     addStringLogger(stream_buffer);
-    const auto& schedule = make_schedule(deck_string, /*slave_mode=*/false);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
     checkLastLineStringBuffer(
         stream_buffer,
         "Slave reservoir 'RES-1' already defined. Redefining",
@@ -159,32 +194,23 @@ SLAVES
     );
     removeStringLogger();
 }
+BOOST_AUTO_TEST_SUITE_END()
 
-// -------------------------------
-// Testing GRUPMAST keyword
-// -------------------------------
+// ------------------------------------------------
+// Testing GRUPMAST keyword (sorted alphabetically)
+// ------------------------------------------------
 
-BOOST_AUTO_TEST_CASE(GRUPMAST_OK) {
-    std::string deck_string = R"(
+BOOST_AUTO_TEST_SUITE(GrupMastTests)
 
+BOOST_AUTO_TEST_CASE(FAIL_MISSING_MASTER_GROUP) {
+        std::string deck_string = R"(
 SCHEDULE
+
 SLAVES
   'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
   'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
 /
 
-GRUPTREE
- 'PLAT-A' 'FIELD' /
-
- 'MOD1'   'PLAT-A' /
-
- 'B1_M'   'MOD1' /
- 'D1_M'   'MOD1' /
- 'C1_M'   'MOD1' /
-
- 'E1_M'   'PLAT-A' /
-/
-
 GRUPMAST
   'D1_M' 'RES-1'  'MANI-D'  1*  /
   'B1_M' 'RES-1'  'MANI-B'  1*  /
@@ -193,23 +219,24 @@ GRUPMAST
 /
 )";
 
-    const auto& schedule = make_schedule(deck_string, /*slave_mode=*/false);
-    const auto& rescoup = schedule[0].rescoup();
-    BOOST_CHECK(rescoup.hasMasterGroup("D1_M"));
-    auto master_group = rescoup.masterGroup("D1_M");
-    BOOST_CHECK_EQUAL(master_group.name(), "D1_M");
-    BOOST_CHECK_EQUAL(master_group.slaveName(), "RES-1");
-    BOOST_CHECK_EQUAL(master_group.slaveGroupName(), "MANI-D");
-    BOOST_CHECK_EQUAL(master_group.flowLimitFraction(), 1e+20);
+    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 9\nGroup 'D1_M': Not defined. Master groups should be defined in advance by using GRUPTREE before referenced in GRUPMAST.");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPMAST_FAIL_MISSING_MASTER_GROUP) {
+BOOST_AUTO_TEST_CASE(FAIL_MISSING_SLAVE) {
         std::string deck_string = R"(
+
 SCHEDULE
 
-SLAVES
-  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
-  'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
+GRUPTREE
+ 'PLAT-A' 'FIELD' /
+
+ 'MOD1'   'PLAT-A' /
+
+ 'B1_M'   'MOD1' /
+ 'D1_M'   'MOD1' /
+ 'C1_M'   'MOD1' /
+
+ 'E1_M'   'PLAT-A' /
 /
 
 GRUPMAST
@@ -220,10 +247,10 @@ GRUPMAST
 /
 )";
 
-    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 9\nGroup 'D1_M': Not defined. Master groups should be defined in advance by using GRUPTREE before referenced in GRUPMAST.");
+    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 17\nSlave reservoir 'RES-1': Not defined. Slave reservoirs should be defined in advance by using SLAVES before referenced in GRUPMAST.");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPMAST_FAIL_SUBORDINATE_GROUPS) {
+BOOST_AUTO_TEST_CASE(FAIL_SUBORDINATE_GROUPS) {
         std::string deck_string = R"(
 SCHEDULE
 
@@ -255,7 +282,7 @@ GRUPMAST
     assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 21\nGroup 'FIELD' has subgroups: A master group cannot contain any wells or subordinate groups.");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPMAST_FAIL_SUBORDINATE_WELLS) {
+BOOST_AUTO_TEST_CASE(FAIL_SUBORDINATE_WELLS) {
         std::string deck_string = R"(
 
 SCHEDULE
@@ -292,10 +319,14 @@ GRUPMAST
     assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 26\nGroup 'D1_M' has wells: A master group cannot contain any wells or subordinate groups.");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPMAST_FAIL_MISSING_SLAVE) {
-        std::string deck_string = R"(
+BOOST_AUTO_TEST_CASE(SYNTAX_OK) {
+    std::string deck_string = R"(
 
 SCHEDULE
+SLAVES
+  'RES-1'  'RC-01_MOD1_PRED'   1*  '../mod1'  4 /
+  'RES-2'  'RC-01_MOD2_PRED'   1*  '../mod2'  1 /
+/
 
 GRUPTREE
  'PLAT-A' 'FIELD' /
@@ -317,13 +348,25 @@ GRUPMAST
 /
 )";
 
-    assertRaisesInputErrorException(deck_string, /*slave_mode=*/false, /*exception_string=*/"Problem with keyword GRUPMAST\nIn <memory string> line 17\nSlave reservoir 'RES-1': Not defined. Slave reservoirs should be defined in advance by using SLAVES before referenced in GRUPMAST.");
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
+    const auto& rescoup = schedule[0].rescoup();
+    BOOST_CHECK(rescoup.hasMasterGroup("D1_M"));
+    auto master_group = rescoup.masterGroup("D1_M");
+    BOOST_CHECK_EQUAL(master_group.name(), "D1_M");
+    BOOST_CHECK_EQUAL(master_group.slaveName(), "RES-1");
+    BOOST_CHECK_EQUAL(master_group.slaveGroupName(), "MANI-D");
+    BOOST_CHECK_EQUAL(master_group.flowLimitFraction(), 1e+20);
 }
 
-// -------------------------------
-// Testing GRUPSLAV keyword
-// -------------------------------
-BOOST_AUTO_TEST_CASE(GRUPSLAV_OK) {
+BOOST_AUTO_TEST_SUITE_END()
+
+// ------------------------------------------------
+// Testing GRUPSLAV keyword (sorted alphabetically)
+// ------------------------------------------------
+
+BOOST_AUTO_TEST_SUITE(GrupSlavTests)
+
+BOOST_AUTO_TEST_CASE(DEFAULT_APPLIED) {
     std::string deck_string = R"(
 
 SCHEDULE
@@ -335,28 +378,21 @@ GRUPTREE
 /
 
 GRUPSLAV
- 'MANI-D'  'D1_M' /
+ 'MANI-D'  1* /
  'MANI-B'  'B1_M' /
  'MANI-C'  'C1_M' /
 /
 )";
 
-    const auto& schedule = make_schedule(deck_string, /*slave_mode=*/true);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/true);
     const auto& rescoup = schedule[0].rescoup();
     BOOST_CHECK(rescoup.hasGrupSlav("MANI-D"));
     auto grup_slav = rescoup.grupSlav("MANI-D");
     BOOST_CHECK_EQUAL(grup_slav.name(), "MANI-D");
-    BOOST_CHECK_EQUAL(grup_slav.masterGroupName(), "D1_M");
-    BOOST_CHECK_EQUAL(grup_slav.oilProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.liquidProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.gasProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.fluidVolumeProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.oilInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.waterInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
-    BOOST_CHECK_EQUAL(grup_slav.gasInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.masterGroupName(), "MANI-D");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPSLAV_FAIL_MISSING_GROUP) {
+BOOST_AUTO_TEST_CASE(FAIL_MISSING_GROUP) {
     std::string deck_string = R"(
 
 SCHEDULE
@@ -370,7 +406,7 @@ GRUPSLAV
     assertRaisesInputErrorException(deck_string, /*slave_mode=*/true, /*exception_string=*/"Problem with keyword GRUPSLAV\nIn <memory string> line 4\nGroup 'MANI-D': Not defined. Slave groups should be defined in advance by using GRUPTREE or WELSPECS before referenced in GRUPSLAV.");
 }
 
-BOOST_AUTO_TEST_CASE(GRUPSLAV_DEFAULT_APPLIED) {
+BOOST_AUTO_TEST_CASE(SYNTAX_OK) {
     std::string deck_string = R"(
 
 SCHEDULE
@@ -382,16 +418,106 @@ GRUPTREE
 /
 
 GRUPSLAV
- 'MANI-D'  1* /
+ 'MANI-D'  'D1_M' /
  'MANI-B'  'B1_M' /
  'MANI-C'  'C1_M' /
 /
 )";
 
-    const auto& schedule = make_schedule(deck_string, /*slave_mode=*/true);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/true);
     const auto& rescoup = schedule[0].rescoup();
     BOOST_CHECK(rescoup.hasGrupSlav("MANI-D"));
     auto grup_slav = rescoup.grupSlav("MANI-D");
     BOOST_CHECK_EQUAL(grup_slav.name(), "MANI-D");
-    BOOST_CHECK_EQUAL(grup_slav.masterGroupName(), "MANI-D");
+    BOOST_CHECK_EQUAL(grup_slav.masterGroupName(), "D1_M");
+    BOOST_CHECK_EQUAL(grup_slav.oilProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.liquidProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.gasProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.fluidVolumeProdFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.oilInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.waterInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+    BOOST_CHECK_EQUAL(grup_slav.gasInjFlag(), Opm::ReservoirCoupling::GrupSlav::FilterFlag::MAST);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+// ------------------------------------------------
+// Testing RCMASTS keyword (sorted alphabetically)
+// ------------------------------------------------
+
+BOOST_AUTO_TEST_SUITE(MinimumMasterTimeStep)
+
+BOOST_AUTO_TEST_CASE(DEFAULT_APPLIED1) {
+    std::string end_of_deck_string = R"(
+TUNING
+-- TSINIT TSMAXZ TSMINZ
+    *       *      0.1   /
+/
+/
+)";
+    std::string deck_string = getMinimumMasterTimeStepDeckString(end_of_deck_string);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
+    const auto& rescoup = schedule[0].rescoup();
+    BOOST_CHECK(rescoup.masterMinTimeStep() == 0.0); // Default value when RCMASTS is not given
+
+}
+
+BOOST_AUTO_TEST_CASE(DEFAULT_APPLIED2) {
+    std::string end_of_deck_string = R"(
+TUNING
+-- TSINIT TSMAXZ TSMINZ
+    *       *      0.1   /
+/
+/
+
+RCMASTS
+  * /
+)";
+    std::string deck_string = getMinimumMasterTimeStepDeckString(end_of_deck_string);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
+    const auto& rescoup = schedule[0].rescoup();
+    const auto& tuning = schedule[0].tuning();
+    // Default value when RCMASTS is given but no value is provided
+    BOOST_CHECK(rescoup.masterMinTimeStep() == tuning.TSMINZ);
+
+}
+
+BOOST_AUTO_TEST_CASE(VALUE_PROVIDED) {
+    std::string end_of_deck_string = R"(
+TUNING
+-- TSINIT TSMAXZ TSMINZ
+    *       *      0.1   /
+/
+/
+
+RCMASTS
+  0.0001 /
+)";
+    std::string deck_string = getMinimumMasterTimeStepDeckString(end_of_deck_string);
+    const auto& schedule = makeSchedule(deck_string, /*slave_mode=*/false);
+    const auto& rescoup = schedule[0].rescoup();
+    // NOTE: Metric unit system is used by default, to time is in days
+    BOOST_CHECK(rescoup.masterMinTimeStep() == (0.0001 * Opm::unit::day));
+}
+
+BOOST_AUTO_TEST_CASE(NEGATIVE_VALUE_PROVIDED) {
+    std::string end_of_deck_string = R"(
+TUNING
+-- TSINIT TSMAXZ TSMINZ
+    *       *      0.1   /
+/
+/
+
+RCMASTS
+  -0.1 /
+)";
+    std::string deck_string = getMinimumMasterTimeStepDeckString(end_of_deck_string);
+    assertRaisesInputErrorException(
+        deck_string,
+        /*slave_mode=*/false,
+        /*exception_string=*/"Problem with keyword RCMASTS\nIn <memory string> line 34\nNegative value for RCMASTS is not allowed."
+    );
+
 }
+
+BOOST_AUTO_TEST_SUITE_END()