diff --git a/external/resinsight/LibCore/cvfColor3.h b/external/resinsight/LibCore/cvfColor3.h
index c270af040..f766c580b 100644
--- a/external/resinsight/LibCore/cvfColor3.h
+++ b/external/resinsight/LibCore/cvfColor3.h
@@ -112,7 +112,7 @@ public:
     Color3f();
     Color3f(float r, float g, float b);
     Color3f(const Color3f& other);
-    Color3f(ColorIdent colorIdent);
+    explicit Color3f(ColorIdent colorIdent);
     explicit Color3f(const Color3ub& other);
 
     Color3f&        operator=(const Color3f& rhs);
@@ -158,7 +158,7 @@ public:
     Color3ub();
     Color3ub(ubyte r, ubyte g, ubyte b);
     Color3ub(const Color3ub& other);
-    Color3ub(ColorIdent colorIdent);
+    explicit Color3ub(ColorIdent colorIdent);
     explicit Color3ub(const Color3f& other);
 
     Color3ub&       operator=(const Color3ub& rhs);
diff --git a/external/resinsight/LibCore/cvfDebugTimer.h b/external/resinsight/LibCore/cvfDebugTimer.h
index 2a6a64d9c..20ca6a1a0 100644
--- a/external/resinsight/LibCore/cvfDebugTimer.h
+++ b/external/resinsight/LibCore/cvfDebugTimer.h
@@ -60,7 +60,7 @@ public:
     };
 
 public:
-    DebugTimer(const char* prefix, OperationMode operationMode = NORMAL);
+    explicit DebugTimer(const char* prefix, OperationMode operationMode = NORMAL);
     ~DebugTimer();
 
     void    restart(const char* msg = NULL);
diff --git a/external/resinsight/LibCore/cvfFlags.h b/external/resinsight/LibCore/cvfFlags.h
index 600f4c4b1..2418d3fc4 100644
--- a/external/resinsight/LibCore/cvfFlags.h
+++ b/external/resinsight/LibCore/cvfFlags.h
@@ -52,7 +52,7 @@ class Flags
 public:
     inline Flags(); 
     inline Flags(const Flags& other);
-    inline Flags(FlagEnum flag);
+    explicit inline Flags(FlagEnum flag);
 
     inline Flags&  operator=(const Flags& rhs);
     inline Flags&  operator=(FlagEnum flag);
diff --git a/external/resinsight/LibCore/cvfObject.h b/external/resinsight/LibCore/cvfObject.h
index 88cc56e97..7314f4efb 100644
--- a/external/resinsight/LibCore/cvfObject.h
+++ b/external/resinsight/LibCore/cvfObject.h
@@ -99,7 +99,7 @@ class ref
 public:
     ref(T* object = NULL);
     ref(const ref& other);
-    template<typename T2> ref(const ref<T2>& other);
+    template<typename T2> explicit ref(const ref<T2>& other);
     ~ref();
 
     ref&                        operator=(T* rhs);
@@ -150,7 +150,7 @@ class cref
 public:
     cref(const T* object = NULL);
     cref(const cref& other);
-    template<typename T2> cref(const cref<T2>& other);
+    template<typename T2> explicit cref(const cref<T2>& other);
     ~cref();
 
     cref&                       operator=(const T* rhs);
diff --git a/external/resinsight/cafPdmCore/cafSignal.h b/external/resinsight/cafPdmCore/cafSignal.h
index 8811437eb..0a3265403 100644
--- a/external/resinsight/cafPdmCore/cafSignal.h
+++ b/external/resinsight/cafPdmCore/cafSignal.h
@@ -108,7 +108,7 @@ public:
     using MemberCallbackAndActiveFlag = std::pair<MemberCallback, bool>;
 
 public:
-    Signal( const SignalEmitter* emitter )
+    explicit Signal( const SignalEmitter* emitter )
         : m_emitter( emitter )
     {
         m_emitter->addEmittedSignal( this );
diff --git a/opm/input/eclipse/Deck/DeckRecord.hpp b/opm/input/eclipse/Deck/DeckRecord.hpp
index 017967d29..afbd88199 100644
--- a/opm/input/eclipse/Deck/DeckRecord.hpp
+++ b/opm/input/eclipse/Deck/DeckRecord.hpp
@@ -34,7 +34,7 @@ namespace Opm {
         typedef std::vector< DeckItem >::const_iterator const_iterator;
 
         DeckRecord() = default;
-        DeckRecord( std::vector< DeckItem >&& items, const bool check_for_duplicate_names = true );
+        explicit DeckRecord( std::vector< DeckItem >&& items, const bool check_for_duplicate_names = true );
 
         static DeckRecord serializationTestObject();
 
diff --git a/opm/input/eclipse/Deck/DeckTree.hpp b/opm/input/eclipse/Deck/DeckTree.hpp
index 1abcd7d30..3b949b6bf 100644
--- a/opm/input/eclipse/Deck/DeckTree.hpp
+++ b/opm/input/eclipse/Deck/DeckTree.hpp
@@ -38,7 +38,7 @@ namespace Opm {
 class DeckTree {
 public:
     DeckTree() = default;
-    DeckTree(const std::string&);
+    explicit DeckTree(const std::string&);
 
     const std::string& parent(const std::string& fname) const;
     bool includes(const std::string& parent_file, const std::string& include_file) const;
diff --git a/opm/input/eclipse/Deck/DeckView.hpp b/opm/input/eclipse/Deck/DeckView.hpp
index 0e40caa23..486fc8da7 100644
--- a/opm/input/eclipse/Deck/DeckView.hpp
+++ b/opm/input/eclipse/Deck/DeckView.hpp
@@ -33,7 +33,7 @@ public:
 
 
     struct Iterator : public storage_type::iterator {
-        Iterator(storage_type::const_iterator inner_iter) :
+        explicit Iterator(storage_type::const_iterator inner_iter) :
             inner(inner_iter)
         {}
 
diff --git a/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.hpp b/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.hpp
index 249ef1ce0..7a989791c 100644
--- a/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.hpp
+++ b/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.hpp
@@ -124,7 +124,7 @@ namespace Opm {
 
         AquiferCT() = default;
         AquiferCT(const TableManager& tables, const Deck& deck);
-        AquiferCT(const std::vector<AquiferCT::AQUCT_data>& data);
+        explicit AquiferCT(const std::vector<AquiferCT::AQUCT_data>& data);
 
         void loadFromRestart(const RestartIO::RstAquifer& rst,
                              const TableManager&          tables);
diff --git a/opm/input/eclipse/EclipseState/Grid/EclipseGrid.hpp b/opm/input/eclipse/EclipseState/Grid/EclipseGrid.hpp
index 2cb59f96d..aadb88d0f 100644
--- a/opm/input/eclipse/EclipseState/Grid/EclipseGrid.hpp
+++ b/opm/input/eclipse/EclipseState/Grid/EclipseGrid.hpp
@@ -75,7 +75,7 @@ namespace Opm {
 
         /// EclipseGrid ignores ACTNUM in Deck, and therefore needs ACTNUM
         /// explicitly.  If a null pointer is passed, every cell is active.
-        EclipseGrid(const Deck& deck, const int * actnum = nullptr);
+        explicit EclipseGrid(const Deck& deck, const int * actnum = nullptr);
 
         static bool hasGDFILE(const Deck& deck);
         static bool hasCylindricalKeywords(const Deck& deck);
diff --git a/opm/input/eclipse/EclipseState/Tables/PlymaxTable.hpp b/opm/input/eclipse/EclipseState/Tables/PlymaxTable.hpp
index f2d09480f..0a86fc9ea 100644
--- a/opm/input/eclipse/EclipseState/Tables/PlymaxTable.hpp
+++ b/opm/input/eclipse/EclipseState/Tables/PlymaxTable.hpp
@@ -28,7 +28,7 @@ namespace Opm {
     class PlymaxTable : public SimpleTable {
         public:
 
-        PlymaxTable( const DeckRecord& record );
+        explicit PlymaxTable(const DeckRecord& record);
 
         const TableColumn& getPolymerConcentrationColumn() const;
         const TableColumn& getMaxPolymerConcentrationColumn() const;
diff --git a/opm/input/eclipse/EclipseState/Tables/PlyrockTable.hpp b/opm/input/eclipse/EclipseState/Tables/PlyrockTable.hpp
index 86059987e..122a1d5bc 100644
--- a/opm/input/eclipse/EclipseState/Tables/PlyrockTable.hpp
+++ b/opm/input/eclipse/EclipseState/Tables/PlyrockTable.hpp
@@ -23,13 +23,13 @@
 
 namespace Opm {
 
-    class DeckReckord;
+    class DeckRecord;
 
     class PlyrockTable : public SimpleTable {
     public:
 
         // This is not really a table; every column has only one element.
-        PlyrockTable( const DeckRecord& record );
+        explicit PlyrockTable(const DeckRecord& record);
 
         // since this keyword is not necessarily monotonic, it cannot be evaluated!
         //using SimpleTable::evaluate;
diff --git a/opm/input/eclipse/Generator/KeywordGenerator.hpp b/opm/input/eclipse/Generator/KeywordGenerator.hpp
index aa7af85a2..d22f7f787 100644
--- a/opm/input/eclipse/Generator/KeywordGenerator.hpp
+++ b/opm/input/eclipse/Generator/KeywordGenerator.hpp
@@ -30,7 +30,7 @@ namespace Opm {
     class KeywordGenerator {
 
     public:
-        KeywordGenerator(bool verbose);
+        explicit KeywordGenerator(bool verbose);
 
         static void ensurePath( const std::string& file_name);
         static std::string endTest();
diff --git a/opm/input/eclipse/Schedule/Action/State.hpp b/opm/input/eclipse/Schedule/Action/State.hpp
index 68040f3ec..34bfaa4c5 100644
--- a/opm/input/eclipse/Schedule/Action/State.hpp
+++ b/opm/input/eclipse/Schedule/Action/State.hpp
@@ -42,7 +42,7 @@ class State {
 struct RunState {
     RunState() = default;
 
-    RunState(std::time_t sim_time)
+    explicit RunState(std::time_t sim_time)
         : run_count(1)
         , last_run(sim_time)
     {}
diff --git a/opm/input/eclipse/Schedule/CompletedCells.hpp b/opm/input/eclipse/Schedule/CompletedCells.hpp
index 907d4a802..38d822d99 100644
--- a/opm/input/eclipse/Schedule/CompletedCells.hpp
+++ b/opm/input/eclipse/Schedule/CompletedCells.hpp
@@ -121,7 +121,7 @@ public:
     };
 
     CompletedCells() = default;
-    CompletedCells(const GridDims& dims);
+    explicit CompletedCells(const GridDims& dims);
     CompletedCells(std::size_t nx, std::size_t ny, std::size_t nz);
     const Cell& get(std::size_t i, std::size_t j, std::size_t k) const;
     std::pair<bool, Cell&> try_get(std::size_t i, std::size_t j, std::size_t k);
diff --git a/opm/input/eclipse/Schedule/GasLiftOpt.hpp b/opm/input/eclipse/Schedule/GasLiftOpt.hpp
index 48920cb6d..4ef1c711f 100644
--- a/opm/input/eclipse/Schedule/GasLiftOpt.hpp
+++ b/opm/input/eclipse/Schedule/GasLiftOpt.hpp
@@ -31,7 +31,7 @@ class GasLiftGroup {
 public:
     GasLiftGroup() = default;
 
-    GasLiftGroup(const std::string& name) :
+    explicit GasLiftGroup(const std::string& name) :
         m_name(name)
     {}
 
diff --git a/opm/input/eclipse/Schedule/Group/GuideRate.hpp b/opm/input/eclipse/Schedule/Group/GuideRate.hpp
index 780fb4309..6a5d5fc44 100644
--- a/opm/input/eclipse/Schedule/Group/GuideRate.hpp
+++ b/opm/input/eclipse/Schedule/Group/GuideRate.hpp
@@ -111,7 +111,7 @@ public:
         GuideRateModel::Target target { GuideRateModel::Target::NONE };
     };
 
-    GuideRate(const Schedule& schedule);
+    explicit GuideRate(const Schedule& schedule);
 
     void setSerializationTestData();
 
diff --git a/opm/input/eclipse/Schedule/MSW/AICD.hpp b/opm/input/eclipse/Schedule/MSW/AICD.hpp
index 4e93f3d6a..d2dbd90dc 100644
--- a/opm/input/eclipse/Schedule/MSW/AICD.hpp
+++ b/opm/input/eclipse/Schedule/MSW/AICD.hpp
@@ -35,7 +35,7 @@ namespace Opm {
     class AutoICD : public SICD {
     public:
         AutoICD() = default;
-        AutoICD(const DeckRecord& record);
+        explicit AutoICD(const DeckRecord& record);
 
         static AutoICD serializationTestObject();
 
diff --git a/opm/input/eclipse/Schedule/MSW/Segment.hpp b/opm/input/eclipse/Schedule/MSW/Segment.hpp
index 86478eed1..0177582ad 100644
--- a/opm/input/eclipse/Schedule/MSW/Segment.hpp
+++ b/opm/input/eclipse/Schedule/MSW/Segment.hpp
@@ -90,7 +90,7 @@ namespace Opm {
                 const double x_in,
                 const double y_in);
 
-        Segment(const RestartIO::RstSegment& rst_segment);
+        explicit Segment(const RestartIO::RstSegment& rst_segment);
 
         static Segment serializationTestObject();
 
diff --git a/opm/input/eclipse/Schedule/Network/Node.hpp b/opm/input/eclipse/Schedule/Network/Node.hpp
index fb7a7f5ff..0368243a4 100644
--- a/opm/input/eclipse/Schedule/Network/Node.hpp
+++ b/opm/input/eclipse/Schedule/Network/Node.hpp
@@ -30,7 +30,7 @@ namespace Network {
 class Node {
 public:
     Node() = default;
-    Node(const std::string& name);
+    explicit Node(const std::string& name);
 
     const std::string& name() const;
     const std::optional<double>& terminal_pressure() const;
diff --git a/opm/input/eclipse/Schedule/UDQ/UDQState.hpp b/opm/input/eclipse/Schedule/UDQ/UDQState.hpp
index 736f088c7..b681c3b73 100644
--- a/opm/input/eclipse/Schedule/UDQ/UDQState.hpp
+++ b/opm/input/eclipse/Schedule/UDQ/UDQState.hpp
@@ -38,7 +38,7 @@ class UDQState
 {
 public:
     UDQState() = default;
-    UDQState(double undefined);
+    explicit UDQState(double undefined);
 
     bool has(const std::string& key) const;
     void load_rst(const RestartIO::RstState& rst_state);
diff --git a/opm/input/eclipse/Schedule/Well/WellInjectionControls.hpp b/opm/input/eclipse/Schedule/Well/WellInjectionControls.hpp
index 92cd47c02..bee84043b 100644
--- a/opm/input/eclipse/Schedule/Well/WellInjectionControls.hpp
+++ b/opm/input/eclipse/Schedule/Well/WellInjectionControls.hpp
@@ -28,7 +28,7 @@ namespace Opm {
 
 struct WellInjectionControls {
 public:
-    WellInjectionControls(int controls_arg) :
+    explicit WellInjectionControls(int controls_arg) :
         controls(controls_arg)
     {}
 
diff --git a/opm/input/eclipse/Schedule/Well/WellProductionControls.hpp b/opm/input/eclipse/Schedule/Well/WellProductionControls.hpp
index b94e7d3a4..e277a289a 100644
--- a/opm/input/eclipse/Schedule/Well/WellProductionControls.hpp
+++ b/opm/input/eclipse/Schedule/Well/WellProductionControls.hpp
@@ -28,7 +28,7 @@ namespace Opm {
 
 struct WellProductionControls {
 public:
-    WellProductionControls(int controls_arg) :
+    explicit WellProductionControls(int controls_arg) :
         controls(controls_arg)
     {
     }
diff --git a/opm/input/eclipse/Units/Dimension.hpp b/opm/input/eclipse/Units/Dimension.hpp
index 424a0f8b4..1244cf74a 100644
--- a/opm/input/eclipse/Units/Dimension.hpp
+++ b/opm/input/eclipse/Units/Dimension.hpp
@@ -27,8 +27,8 @@ namespace Opm {
     class Dimension {
     public:
         Dimension();
-        Dimension(double SIfactor,
-                  double SIoffset = 0.0);
+        explicit Dimension(double SIfactor,
+                           double SIoffset = 0.0);
 
         static Dimension serializationTestObject();
 
diff --git a/opm/io/eclipse/ERsm.hpp b/opm/io/eclipse/ERsm.hpp
index d44c00b79..1318e6888 100644
--- a/opm/io/eclipse/ERsm.hpp
+++ b/opm/io/eclipse/ERsm.hpp
@@ -56,7 +56,7 @@ struct Vector{
 
 
 public:
-    ERsm(const std::string& fname);
+    explicit ERsm(const std::string& fname);
 
     const std::vector<TimeStampUTC>& dates() const;
     const std::vector<double>& days() const;
diff --git a/opm/io/eclipse/rst/action.hpp b/opm/io/eclipse/rst/action.hpp
index f18e61ba0..452aa9d50 100644
--- a/opm/io/eclipse/rst/action.hpp
+++ b/opm/io/eclipse/rst/action.hpp
@@ -39,8 +39,8 @@ struct RstAction {
 
         Quantity() = default;
         Quantity(const std::string * zacn, double sacn_value);
-        Quantity(const std::string& quantity);
-        Quantity(double value);
+        explicit Quantity(const std::string& quantity);
+        explicit Quantity(double value);
     };
 
 
diff --git a/src/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.cpp b/src/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.cpp
index 97e22b038..7fc34073a 100644
--- a/src/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.cpp
+++ b/src/opm/input/eclipse/EclipseState/Aquifer/AquiferCT.cpp
@@ -264,7 +264,7 @@ void AquiferCT::loadFromRestart(const RestartIO::RstAquifer& rst,
 
 AquiferCT AquiferCT::serializationTestObject()
 {
-    return { { AQUCT_data::serializationTestObject() } };
+    return AquiferCT{ { AQUCT_data::serializationTestObject() } };
 }
 
 std::size_t AquiferCT::size() const {
diff --git a/src/opm/input/eclipse/Parser/ParserRecord.cpp b/src/opm/input/eclipse/Parser/ParserRecord.cpp
index a35d7d5ea..f1a4cf31d 100644
--- a/src/opm/input/eclipse/Parser/ParserRecord.cpp
+++ b/src/opm/input/eclipse/Parser/ParserRecord.cpp
@@ -136,7 +136,7 @@ namespace {
             parseContext.handleError(ParseContext::PARSE_EXTRA_DATA , msg_format, location, errors);
         }
 
-        return { std::move( items ), false };
+        return DeckRecord{ std::move( items ), false };
     }
 
     bool ParserRecord::equal(const ParserRecord& other) const {