diff --git a/arangod/Pregel/Algos/AsyncSCC.cpp b/arangod/Pregel/Algos/AsyncSCC.cpp
index a644b16619..0bd0806fc8 100644
--- a/arangod/Pregel/Algos/AsyncSCC.cpp
+++ b/arangod/Pregel/Algos/AsyncSCC.cpp
@@ -154,7 +154,7 @@ struct SCCGraphFormat : public GraphFormat<SCCValue, int8_t> {
   const std::string _resultField;
   uint64_t vertexIdRange = 0;
 
-  SCCGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit SCCGraphFormat(std::string const& result) : _resultField(result) {}
 
   void willLoadVertices(uint64_t count) override {
     // if we aren't running in a cluster it doesn't matter
diff --git a/arangod/Pregel/Algos/AsyncSCC.h b/arangod/Pregel/Algos/AsyncSCC.h
index 9262818b45..2fe7096bad 100644
--- a/arangod/Pregel/Algos/AsyncSCC.h
+++ b/arangod/Pregel/Algos/AsyncSCC.h
@@ -47,7 +47,7 @@ namespace algos {
 struct AsyncSCC
     : public SimpleAlgorithm<SCCValue, int8_t, SenderMessage<uint64_t>> {
  public:
-  AsyncSCC(VPackSlice userParams)
+  explicit AsyncSCC(VPackSlice userParams)
       : SimpleAlgorithm<SCCValue, int8_t, SenderMessage<uint64_t>>(
             "AsyncSCC", userParams) {}
 
diff --git a/arangod/Pregel/Algos/ConnectedComponents.cpp b/arangod/Pregel/Algos/ConnectedComponents.cpp
index 0baf5d6214..d979c8c851 100644
--- a/arangod/Pregel/Algos/ConnectedComponents.cpp
+++ b/arangod/Pregel/Algos/ConnectedComponents.cpp
@@ -56,7 +56,7 @@ ConnectedComponents::createComputation(WorkerConfig const* config) const {
 struct MyGraphFormat : public VertexGraphFormat<int64_t, int64_t> {
   uint64_t vertexIdRange = 0;
 
-  MyGraphFormat(std::string const& result)
+  explicit MyGraphFormat(std::string const& result)
       : VertexGraphFormat<int64_t, int64_t>(result, 0) {}
 
   void willLoadVertices(uint64_t count) override {
diff --git a/arangod/Pregel/Algos/ConnectedComponents.h b/arangod/Pregel/Algos/ConnectedComponents.h
index bbaae547b8..e6b73a1b2e 100644
--- a/arangod/Pregel/Algos/ConnectedComponents.h
+++ b/arangod/Pregel/Algos/ConnectedComponents.h
@@ -36,7 +36,7 @@ namespace algos {
 /// doesn't necessarily leads to a correct result on unidirected graphs
 struct ConnectedComponents : public SimpleAlgorithm<int64_t, int64_t, int64_t> {
  public:
-  ConnectedComponents(VPackSlice userParams)
+  explicit ConnectedComponents(VPackSlice userParams)
       : SimpleAlgorithm("ConnectedComponents", userParams) {}
 
   bool supportsAsyncMode() const override { return true; }
diff --git a/arangod/Pregel/Algos/DMID/DMID.cpp b/arangod/Pregel/Algos/DMID/DMID.cpp
index aef27a8793..0d70af5e31 100644
--- a/arangod/Pregel/Algos/DMID/DMID.cpp
+++ b/arangod/Pregel/Algos/DMID/DMID.cpp
@@ -584,7 +584,7 @@ struct DMIDGraphFormat : public GraphFormat<DMIDValue, float> {
   const std::string _resultField;
   uint64_t vertexIdRange = 0;
 
-  DMIDGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit DMIDGraphFormat(std::string const& result) : _resultField(result) {}
 
   void willLoadVertices(uint64_t count) override {
     // if we aren't running in a cluster it doesn't matter
diff --git a/arangod/Pregel/Algos/DMID/DMID.h b/arangod/Pregel/Algos/DMID/DMID.h
index 53889056d1..1a9ff7ca13 100644
--- a/arangod/Pregel/Algos/DMID/DMID.h
+++ b/arangod/Pregel/Algos/DMID/DMID.h
@@ -34,7 +34,7 @@ namespace algos {
 struct DMID
     : public SimpleAlgorithm<DMIDValue, float, DMIDMessage> {
  public:
-  DMID(VPackSlice userParams) : SimpleAlgorithm<DMIDValue, float, DMIDMessage>(
+  explicit DMID(VPackSlice userParams) : SimpleAlgorithm<DMIDValue, float, DMIDMessage>(
             "DMID", userParams) {}
 
   GraphFormat<DMIDValue, float>* inputFormat() const override;
diff --git a/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.cpp b/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.cpp
index 7c426879ab..880d5fb864 100644
--- a/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.cpp
+++ b/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.cpp
@@ -90,7 +90,7 @@ EffectiveCloseness::createComputation(WorkerConfig const*) const {
 struct ECGraphFormat : public GraphFormat<ECValue, int8_t> {
   const std::string _resultField;
 
-  ECGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit ECGraphFormat(std::string const& result) : _resultField(result) {}
 
   size_t estimatedEdgeSize() const override { return 0; };
 
diff --git a/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.h b/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.h
index 47fa704953..ea66c64100 100644
--- a/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.h
+++ b/arangod/Pregel/Algos/EffectiveCloseness/EffectiveCloseness.h
@@ -33,7 +33,7 @@ namespace algos {
 /// Effective Closeness
 struct EffectiveCloseness : public SimpleAlgorithm<ECValue, int8_t, HLLCounter> {
   
-  EffectiveCloseness(VPackSlice params)
+  explicit EffectiveCloseness(VPackSlice params)
       : SimpleAlgorithm<ECValue, int8_t, HLLCounter>("EffectiveCloseness", params) {}
 
   GraphFormat<ECValue, int8_t>* inputFormat() const override;
diff --git a/arangod/Pregel/Algos/HITS.cpp b/arangod/Pregel/Algos/HITS.cpp
index 0861405adc..ae97f48ec1 100644
--- a/arangod/Pregel/Algos/HITS.cpp
+++ b/arangod/Pregel/Algos/HITS.cpp
@@ -103,7 +103,7 @@ HITS::createComputation(WorkerConfig const* config) const {
 struct HITSGraphFormat : public GraphFormat<HITSValue, int8_t> {
   const std::string _resultField;
 
-  HITSGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit HITSGraphFormat(std::string const& result) : _resultField(result) {}
 
   size_t estimatedEdgeSize() const override { return 0; };
 
diff --git a/arangod/Pregel/Algos/HITS.h b/arangod/Pregel/Algos/HITS.h
index c9a262aa0a..7cd048bb4a 100644
--- a/arangod/Pregel/Algos/HITS.h
+++ b/arangod/Pregel/Algos/HITS.h
@@ -46,7 +46,7 @@ namespace algos {
 
 struct HITS : public SimpleAlgorithm<HITSValue, int8_t, SenderMessage<double>> {
  public:
-  HITS(VPackSlice userParams)
+  explicit HITS(VPackSlice userParams)
       : SimpleAlgorithm<HITSValue, int8_t, SenderMessage<double>>("HITS",
                                                                   userParams) {}
 
diff --git a/arangod/Pregel/Algos/LabelPropagation.cpp b/arangod/Pregel/Algos/LabelPropagation.cpp
index 6b40931a9d..23e84f0533 100644
--- a/arangod/Pregel/Algos/LabelPropagation.cpp
+++ b/arangod/Pregel/Algos/LabelPropagation.cpp
@@ -107,7 +107,7 @@ struct LPGraphFormat : public GraphFormat<LPValue, int8_t> {
   std::string _resultField;
   uint64_t vertexIdRange = 0;
 
-  LPGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit LPGraphFormat(std::string const& result) : _resultField(result) {}
 
   size_t estimatedVertexSize() const override { return sizeof(LPValue); };
   size_t estimatedEdgeSize() const override { return 0; };
diff --git a/arangod/Pregel/Algos/LabelPropagation.h b/arangod/Pregel/Algos/LabelPropagation.h
index 174fa4ed82..650a3d6a1c 100644
--- a/arangod/Pregel/Algos/LabelPropagation.h
+++ b/arangod/Pregel/Algos/LabelPropagation.h
@@ -40,7 +40,7 @@ namespace algos {
 /// maximum superstep number.
 struct LabelPropagation : public SimpleAlgorithm<LPValue, int8_t, uint64_t> {
  public:
-  LabelPropagation(VPackSlice userParams)
+  explicit LabelPropagation(VPackSlice userParams)
       : SimpleAlgorithm<LPValue, int8_t, uint64_t>("LabelPropagation",
                                                    userParams) {}
 
diff --git a/arangod/Pregel/Algos/LineRank.h b/arangod/Pregel/Algos/LineRank.h
index 90e5509291..2a8cd1bcf8 100644
--- a/arangod/Pregel/Algos/LineRank.h
+++ b/arangod/Pregel/Algos/LineRank.h
@@ -39,7 +39,7 @@ namespace algos {
 /// github.com/JananiC/NetworkCentralities/blob/master/src/main/java/linerank/LineRank.java
 struct LineRank : public SimpleAlgorithm<float, float, float> {
  public:
-  LineRank(arangodb::velocypack::Slice params);
+  explicit LineRank(arangodb::velocypack::Slice params);
 
   GraphFormat<float, float>* inputFormat() const override {
     return new VertexGraphFormat<float, float>(_resultField, -1.0);
diff --git a/arangod/Pregel/Algos/PageRank.h b/arangod/Pregel/Algos/PageRank.h
index f3ecda8886..69611a8c90 100644
--- a/arangod/Pregel/Algos/PageRank.h
+++ b/arangod/Pregel/Algos/PageRank.h
@@ -34,7 +34,7 @@ namespace algos {
 struct PageRank : public SimpleAlgorithm<float, float, float> {
   uint64_t _maxGSS = 250;
 
-  PageRank(arangodb::velocypack::Slice const& params);
+  explicit PageRank(arangodb::velocypack::Slice const& params);
 
   GraphFormat<float, float>* inputFormat() const override {
     return new VertexGraphFormat<float, float>(_resultField, 0);
diff --git a/arangod/Pregel/Algos/RecoveringPageRank.cpp b/arangod/Pregel/Algos/RecoveringPageRank.cpp
index cfb4211d4c..86b20c9dce 100644
--- a/arangod/Pregel/Algos/RecoveringPageRank.cpp
+++ b/arangod/Pregel/Algos/RecoveringPageRank.cpp
@@ -119,7 +119,7 @@ VertexCompensation<float, float, float>* RecoveringPageRank::createCompensation(
 struct RPRMasterContext : public MasterContext {
   float _threshold;
 
-  RPRMasterContext(VPackSlice params) {
+  explicit RPRMasterContext(VPackSlice params) {
     VPackSlice t = params.get("convergenceThreshold");
     _threshold = t.isNumber() ? t.getNumber<float>() : EPS;
   };
diff --git a/arangod/Pregel/Algos/RecoveringPageRank.h b/arangod/Pregel/Algos/RecoveringPageRank.h
index 0a149df2bc..a54bd6960d 100644
--- a/arangod/Pregel/Algos/RecoveringPageRank.h
+++ b/arangod/Pregel/Algos/RecoveringPageRank.h
@@ -32,7 +32,7 @@ namespace algos {
 
 /// PageRank
 struct RecoveringPageRank : public SimpleAlgorithm<float, float, float> {
-  RecoveringPageRank(arangodb::velocypack::Slice params)
+  explicit RecoveringPageRank(arangodb::velocypack::Slice params)
       : SimpleAlgorithm("PageRank", params) {}
 
   bool supportsCompensation() const override { return true; }
diff --git a/arangod/Pregel/Algos/SCC.cpp b/arangod/Pregel/Algos/SCC.cpp
index 7342d1d41c..3a1447f4a9 100644
--- a/arangod/Pregel/Algos/SCC.cpp
+++ b/arangod/Pregel/Algos/SCC.cpp
@@ -148,7 +148,7 @@ struct SCCGraphFormat : public GraphFormat<SCCValue, int8_t> {
   const std::string _resultField;
   uint64_t vertexIdRange = 0;
 
-  SCCGraphFormat(std::string const& result) : _resultField(result) {}
+  explicit SCCGraphFormat(std::string const& result) : _resultField(result) {}
 
   void willLoadVertices(uint64_t count) override {
     // if we aren't running in a cluster it doesn't matter
diff --git a/arangod/Pregel/Algos/SCC.h b/arangod/Pregel/Algos/SCC.h
index 178620a4fa..e1898fcf18 100644
--- a/arangod/Pregel/Algos/SCC.h
+++ b/arangod/Pregel/Algos/SCC.h
@@ -46,7 +46,7 @@ namespace algos {
 
 struct SCC : public SimpleAlgorithm<SCCValue, int8_t, SenderMessage<uint64_t>> {
  public:
-  SCC(VPackSlice userParams)
+  explicit SCC(VPackSlice userParams)
       : SimpleAlgorithm<SCCValue, int8_t, SenderMessage<uint64_t>>(
             "SCC", userParams) {}
 
diff --git a/arangod/Pregel/Algos/SSSP.h b/arangod/Pregel/Algos/SSSP.h
index b7df507f42..caa7099177 100644
--- a/arangod/Pregel/Algos/SSSP.h
+++ b/arangod/Pregel/Algos/SSSP.h
@@ -36,7 +36,7 @@ class SSSPAlgorithm : public Algorithm<int64_t, int64_t, int64_t> {
   std::string _sourceDocumentId, _resultField = "result";
 
  public:
-  SSSPAlgorithm(VPackSlice userParams) : Algorithm("SSSP") {
+  explicit SSSPAlgorithm(VPackSlice userParams) : Algorithm("SSSP") {
       if (!userParams.isObject() || !userParams.hasKey("source")) {
         THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER,
                                        "You need to specify the source document id");
diff --git a/arangod/Pregel/Algos/ShortestPath.cpp b/arangod/Pregel/Algos/ShortestPath.cpp
index b05461794b..beca094993 100644
--- a/arangod/Pregel/Algos/ShortestPath.cpp
+++ b/arangod/Pregel/Algos/ShortestPath.cpp
@@ -37,7 +37,7 @@ static std::string const spUpperPathBound = "bound";
 struct SPComputation : public VertexComputation<int64_t, int64_t, int64_t> {
   PregelID _target;
 
-  SPComputation(PregelID const& target) : _target(target) {}
+  explicit SPComputation(PregelID const& target) : _target(target) {}
   void compute(MessageIterator<int64_t> const& messages) override {
     int64_t current = vertexData();
     for (const int64_t* msg : messages) {
diff --git a/arangod/Pregel/IncomingCache.h b/arangod/Pregel/IncomingCache.h
index 1cedfa3674..fda288f858 100644
--- a/arangod/Pregel/IncomingCache.h
+++ b/arangod/Pregel/IncomingCache.h
@@ -53,7 +53,7 @@ class InCache {
 
   /// Initialize format and mutex map.
   /// @param config can be null if you don't want locks
-  InCache(MessageFormat<M> const* format);
+  explicit InCache(MessageFormat<M> const* format);
   virtual void _set(PregelShard shard, PregelKey const& vertexId,
                     M const& data) = 0;
 
diff --git a/arangod/Pregel/ThreadPool.h b/arangod/Pregel/ThreadPool.h
index c161dc5df8..cbf1a8fa64 100644
--- a/arangod/Pregel/ThreadPool.h
+++ b/arangod/Pregel/ThreadPool.h
@@ -95,7 +95,7 @@ class WorkerThread : public arangodb::Thread {
   WorkerThread(WorkerThread const&) = delete;
   WorkerThread operator=(WorkerThread const&) = delete;
 
-  WorkerThread(ThreadPool* pool)
+  explicit WorkerThread(ThreadPool* pool)
       : Thread(pool->name()), _pool(pool), _status(0) {}
 
   ~WorkerThread() {