diff --git a/src/lib/base/Log.h b/src/lib/base/Log.h
index 412409927..9ce2d51fd 100644
--- a/src/lib/base/Log.h
+++ b/src/lib/base/Log.h
@@ -27,8 +27,8 @@ LOGC() provide convenient access.
 class Log
 {
 public:
-  Log(bool singleton = true);
-  Log(Log *src);
+  explicit Log(bool singleton = true);
+  explicit Log(Log *src);
   Log(Log const &) = delete;
   Log(Log &&) = delete;
   ~Log();
diff --git a/src/lib/base/XBase.h b/src/lib/base/XBase.h
index 7e658ed04..1785f9c80 100644
--- a/src/lib/base/XBase.h
+++ b/src/lib/base/XBase.h
@@ -20,7 +20,7 @@ public:
   //! Use getWhat() as the result of what()
   XBase();
   //! Use \c msg as the result of what()
-  XBase(const std::string &msg);
+  explicit XBase(const std::string &msg);
   ~XBase() throw() override = default;
 
   //! Reason for exception
diff --git a/src/lib/client/Client.h b/src/lib/client/Client.h
index 220c9334a..3da40df0c 100644
--- a/src/lib/client/Client.h
+++ b/src/lib/client/Client.h
@@ -43,7 +43,7 @@ public:
   class FailInfo
   {
   public:
-    FailInfo(const char *what) : m_retry(false), m_what(what)
+    explicit FailInfo(const char *what) : m_retry(false), m_what(what)
     {
       // do nothing
     }
diff --git a/src/lib/deskflow/ArgParser.h b/src/lib/deskflow/ArgParser.h
index f5075a4fe..fd09256ed 100644
--- a/src/lib/deskflow/ArgParser.h
+++ b/src/lib/deskflow/ArgParser.h
@@ -21,7 +21,7 @@ class ArgParser
 {
 
 public:
-  ArgParser(App *app);
+  explicit ArgParser(App *app);
 
   bool parseServerArgs(deskflow::ServerArgs &args, int argc, const char *const *argv);
   bool parseClientArgs(deskflow::ClientArgs &args, int argc, const char *const *argv);
diff --git a/src/lib/deskflow/Chunk.h b/src/lib/deskflow/Chunk.h
index 67627969c..9701d1169 100644
--- a/src/lib/deskflow/Chunk.h
+++ b/src/lib/deskflow/Chunk.h
@@ -12,7 +12,7 @@
 class Chunk : public EventData
 {
 public:
-  Chunk(size_t size);
+  explicit Chunk(size_t size);
   Chunk(Chunk const &) = delete;
   Chunk(Chunk &&) = delete;
   ~Chunk() override;
diff --git a/src/lib/deskflow/ClientApp.h b/src/lib/deskflow/ClientApp.h
index 2f9cce773..0adb0075b 100644
--- a/src/lib/deskflow/ClientApp.h
+++ b/src/lib/deskflow/ClientApp.h
@@ -23,7 +23,7 @@ class ISocketFactory;
 class ClientApp : public App
 {
 public:
-  ClientApp(IEventQueue *events);
+  explicit ClientApp(IEventQueue *events);
   ~ClientApp() override = default;
 
   //
diff --git a/src/lib/deskflow/ClipboardChunk.h b/src/lib/deskflow/ClipboardChunk.h
index 3d4b5c613..46fa66a9f 100644
--- a/src/lib/deskflow/ClipboardChunk.h
+++ b/src/lib/deskflow/ClipboardChunk.h
@@ -21,7 +21,7 @@ class IStream;
 class ClipboardChunk : public Chunk
 {
 public:
-  ClipboardChunk(size_t size);
+  explicit ClipboardChunk(size_t size);
 
   static ClipboardChunk *start(ClipboardID id, uint32_t sequence, const std::string &size);
   static ClipboardChunk *data(ClipboardID id, uint32_t sequence, const std::string &data);
diff --git a/src/lib/deskflow/DisplayInvalidException.h b/src/lib/deskflow/DisplayInvalidException.h
index f6f6f04d5..304d2caf5 100644
--- a/src/lib/deskflow/DisplayInvalidException.h
+++ b/src/lib/deskflow/DisplayInvalidException.h
@@ -12,12 +12,12 @@
 class DisplayInvalidException : public std::runtime_error
 {
 public:
-  DisplayInvalidException(const char *msg) : std::runtime_error(msg)
+  explicit DisplayInvalidException(const char *msg) : std::runtime_error(msg)
   {
     // do nothing
   }
 
-  DisplayInvalidException(std::string msg) : std::runtime_error(msg)
+  explicit DisplayInvalidException(std::string msg) : std::runtime_error(msg)
   {
     // do nothing
   }
diff --git a/src/lib/deskflow/IKeyState.h b/src/lib/deskflow/IKeyState.h
index 6fbc3ea1a..2dfca19af 100644
--- a/src/lib/deskflow/IKeyState.h
+++ b/src/lib/deskflow/IKeyState.h
@@ -23,7 +23,7 @@ to synthesize key events.
 class IKeyState : public IInterface
 {
 public:
-  IKeyState(IEventQueue *events);
+  explicit IKeyState(IEventQueue *events);
 
   enum
   {
diff --git a/src/lib/deskflow/IPlatformScreen.h b/src/lib/deskflow/IPlatformScreen.h
index 7ee577cb2..5cdd9ac3e 100644
--- a/src/lib/deskflow/IPlatformScreen.h
+++ b/src/lib/deskflow/IPlatformScreen.h
@@ -28,7 +28,7 @@ public:
   //! @name manipulators
   //@{
 
-  IPlatformScreen(IEventQueue *events) : IKeyState(events)
+  explicit IPlatformScreen(IEventQueue *events) : IKeyState(events)
   {
     // do nothing
   }
diff --git a/src/lib/deskflow/ServerApp.h b/src/lib/deskflow/ServerApp.h
index b82e11cb9..b95f43310 100644
--- a/src/lib/deskflow/ServerApp.h
+++ b/src/lib/deskflow/ServerApp.h
@@ -45,7 +45,7 @@ class ServerApp : public App
   using ServerConfig = deskflow::server::Config;
 
 public:
-  ServerApp(IEventQueue *events);
+  explicit ServerApp(IEventQueue *events);
   ~ServerApp() override = default;
 
   //
diff --git a/src/lib/deskflow/XDeskflow.h b/src/lib/deskflow/XDeskflow.h
index 926a81bed..b38da1b93 100644
--- a/src/lib/deskflow/XDeskflow.h
+++ b/src/lib/deskflow/XDeskflow.h
@@ -65,7 +65,7 @@ a client that is already connected.
 class XDuplicateClient : public XDeskflow
 {
 public:
-  XDuplicateClient(const std::string &name);
+  explicit XDuplicateClient(const std::string &name);
   ~XDuplicateClient() throw() override = default;
 
   //! @name accessors
@@ -91,7 +91,7 @@ unknown to the server.
 class XUnknownClient : public XDeskflow
 {
 public:
-  XUnknownClient(const std::string &name);
+  explicit XUnknownClient(const std::string &name);
   ~XUnknownClient() throw() override = default;
 
   //! @name accessors
@@ -118,7 +118,7 @@ exit(int).
 class XExitApp : public XDeskflow
 {
 public:
-  XExitApp(int code);
+  explicit XExitApp(int code);
   ~XExitApp() throw() override = default;
 
   //! Get the exit code
diff --git a/src/lib/deskflow/XScreen.h b/src/lib/deskflow/XScreen.h
index c75b79432..bcd212c9b 100644
--- a/src/lib/deskflow/XScreen.h
+++ b/src/lib/deskflow/XScreen.h
@@ -36,7 +36,7 @@ public:
   \c timeUntilRetry is the suggested time the caller should wait until
   trying to open the screen again.
   */
-  XScreenUnavailable(double timeUntilRetry);
+  explicit XScreenUnavailable(double timeUntilRetry);
   ~XScreenUnavailable() throw() override = default;
 
   //! @name manipulators
diff --git a/src/lib/deskflow/unix/AppUtilUnix.h b/src/lib/deskflow/unix/AppUtilUnix.h
index 18f1089f1..e5a703c1a 100644
--- a/src/lib/deskflow/unix/AppUtilUnix.h
+++ b/src/lib/deskflow/unix/AppUtilUnix.h
@@ -16,7 +16,7 @@ class IEventQueue;
 class AppUtilUnix : public AppUtil
 {
 public:
-  AppUtilUnix(IEventQueue *events);
+  explicit AppUtilUnix(IEventQueue *events);
   ~AppUtilUnix() override = default;
 
   int run(int argc, char **argv) override;
diff --git a/src/lib/deskflow/win32/AppUtilWindows.h b/src/lib/deskflow/win32/AppUtilWindows.h
index fd8e94f1b..030118928 100644
--- a/src/lib/deskflow/win32/AppUtilWindows.h
+++ b/src/lib/deskflow/win32/AppUtilWindows.h
@@ -29,7 +29,7 @@ enum AppExitMode
 class AppUtilWindows : public AppUtil
 {
 public:
-  AppUtilWindows(IEventQueue *events);
+  explicit AppUtilWindows(IEventQueue *events);
   ~AppUtilWindows() override;
 
   static AppUtilWindows &instance();
diff --git a/src/lib/gui/widgets/NewScreenWidget.h b/src/lib/gui/widgets/NewScreenWidget.h
index 63bf37951..bedf8143e 100644
--- a/src/lib/gui/widgets/NewScreenWidget.h
+++ b/src/lib/gui/widgets/NewScreenWidget.h
@@ -17,7 +17,7 @@ class NewScreenWidget : public QLabel
   Q_OBJECT
 
 public:
-  NewScreenWidget(QWidget *parent);
+  explicit NewScreenWidget(QWidget *parent);
 
 protected:
   void mousePressEvent(QMouseEvent *event) override;
diff --git a/src/lib/gui/widgets/ScreenSetupView.h b/src/lib/gui/widgets/ScreenSetupView.h
index 3563b0e14..5dc13bbcb 100644
--- a/src/lib/gui/widgets/ScreenSetupView.h
+++ b/src/lib/gui/widgets/ScreenSetupView.h
@@ -23,7 +23,7 @@ class ScreenSetupView : public QTableView
   Q_OBJECT
 
 public:
-  ScreenSetupView(QWidget *parent);
+  explicit ScreenSetupView(QWidget *parent);
 
 public:
   void setModel(QAbstractItemModel *model) override;
diff --git a/src/lib/gui/widgets/TrashScreenWidget.h b/src/lib/gui/widgets/TrashScreenWidget.h
index 4e96fd2e3..a5bf4c45b 100644
--- a/src/lib/gui/widgets/TrashScreenWidget.h
+++ b/src/lib/gui/widgets/TrashScreenWidget.h
@@ -18,7 +18,7 @@ class TrashScreenWidget : public QLabel
   Q_OBJECT
 
 public:
-  TrashScreenWidget(QWidget *parent) : QLabel(parent)
+  explicit TrashScreenWidget(QWidget *parent) : QLabel(parent)
   {
     // do nothing
   }
diff --git a/src/lib/mt/CondVar.h b/src/lib/mt/CondVar.h
index fbde627d6..f49742248 100644
--- a/src/lib/mt/CondVar.h
+++ b/src/lib/mt/CondVar.h
@@ -27,7 +27,7 @@ public:
   associated mutex.  The mutex needn't be unique to one condition
   variable.
   */
-  CondVarBase(Mutex *mutex);
+  explicit CondVarBase(Mutex *mutex);
   ~CondVarBase();
 
   //! @name manipulators
diff --git a/src/lib/mt/Lock.h b/src/lib/mt/Lock.h
index 702aec236..0141a648c 100644
--- a/src/lib/mt/Lock.h
+++ b/src/lib/mt/Lock.h
@@ -23,9 +23,9 @@ class Lock
 {
 public:
   //! Lock the mutex \c mutex
-  Lock(const Mutex *mutex);
+  explicit Lock(const Mutex *mutex);
   //! Lock the condition variable \c cv
-  Lock(const CondVarBase *cv);
+  explicit Lock(const CondVarBase *cv);
   //! Unlock the mutex or condition variable
   ~Lock();
 
diff --git a/src/lib/mt/Thread.h b/src/lib/mt/Thread.h
index acfb9e03d..2593e9e34 100644
--- a/src/lib/mt/Thread.h
+++ b/src/lib/mt/Thread.h
@@ -37,7 +37,7 @@ public:
   Create and start a new thread executing the \c adoptedJob.  The
   new thread takes ownership of \c adoptedJob and will delete it.
   */
-  Thread(IJob *adoptedJob);
+  explicit Thread(IJob *adoptedJob);
 
   //! Duplicate a thread handle
   /*!
@@ -190,7 +190,7 @@ public:
   //@}
 
 private:
-  Thread(ArchThread);
+  explicit Thread(ArchThread);
 
   static void *threadFunc(void *);
 
diff --git a/src/lib/mt/XThread.h b/src/lib/mt/XThread.h
index 9b99188ca..49fa0aad7 100644
--- a/src/lib/mt/XThread.h
+++ b/src/lib/mt/XThread.h
@@ -19,7 +19,7 @@ class XThreadExit : public XThread
 {
 public:
   //! \c result is the result of the thread
-  XThreadExit(void *result) : m_result(result)
+  explicit XThreadExit(void *result) : m_result(result)
   {
     // do nothing
   }
diff --git a/src/lib/net/IDataSocket.h b/src/lib/net/IDataSocket.h
index 2ae8c5cea..19e762310 100644
--- a/src/lib/net/IDataSocket.h
+++ b/src/lib/net/IDataSocket.h
@@ -22,15 +22,16 @@ public:
   class ConnectionFailedInfo
   {
   public:
-    ConnectionFailedInfo(const char *what) : m_what(what)
+    explicit ConnectionFailedInfo(const char *what) : m_what(what)
     {
       // do nothing
     }
     std::string m_what;
   };
 
-  IDataSocket(IEventQueue *events)
+  explicit IDataSocket(IEventQueue *events)
   {
+    // do nothing
   }
 
   //! @name manipulators
diff --git a/src/lib/net/NetworkAddress.h b/src/lib/net/NetworkAddress.h
index 30b88ca0a..c23099c1b 100644
--- a/src/lib/net/NetworkAddress.h
+++ b/src/lib/net/NetworkAddress.h
@@ -26,7 +26,7 @@ public:
   Construct the wildcard address with the given port.  \c port must
   not be zero.
   */
-  NetworkAddress(int port);
+  explicit NetworkAddress(int port);
 
   /*!
   Construct the network address for the given \c hostname and \c port.
diff --git a/src/lib/platform/EiScreen.h b/src/lib/platform/EiScreen.h
index eed7739e7..fa89cfc00 100644
--- a/src/lib/platform/EiScreen.h
+++ b/src/lib/platform/EiScreen.h
@@ -164,7 +164,7 @@ private:
   class HotKeySet
   {
   public:
-    HotKeySet(KeyID keyid);
+    explicit HotKeySet(KeyID keyid);
     KeyID keyid() const
     {
       return id_;
diff --git a/src/lib/platform/XWindowsClipboardBMPConverter.h b/src/lib/platform/XWindowsClipboardBMPConverter.h
index 077b7d8ac..8d5722e50 100644
--- a/src/lib/platform/XWindowsClipboardBMPConverter.h
+++ b/src/lib/platform/XWindowsClipboardBMPConverter.h
@@ -13,7 +13,7 @@
 class XWindowsClipboardBMPConverter : public IXWindowsClipboardConverter
 {
 public:
-  XWindowsClipboardBMPConverter(Display *display);
+  explicit XWindowsClipboardBMPConverter(Display *display);
   ~XWindowsClipboardBMPConverter() override = default;
 
   // IXWindowsClipboardConverter overrides
diff --git a/src/lib/platform/XWindowsUtil.h b/src/lib/platform/XWindowsUtil.h
index 74386cb0b..1e09498a1 100644
--- a/src/lib/platform/XWindowsUtil.h
+++ b/src/lib/platform/XWindowsUtil.h
@@ -125,7 +125,7 @@ public:
     /*!
     Ignore X11 errors.
     */
-    ErrorLock(Display *);
+    explicit ErrorLock(Display *);
     ErrorLock(ErrorLock const &) = delete;
     ErrorLock(ErrorLock &&) = delete;
 
diff --git a/src/lib/server/BaseClientProxy.h b/src/lib/server/BaseClientProxy.h
index 0331a148d..d61e34642 100644
--- a/src/lib/server/BaseClientProxy.h
+++ b/src/lib/server/BaseClientProxy.h
@@ -20,7 +20,7 @@ public:
   /*!
   \c name is the name of the client.
   */
-  BaseClientProxy(const std::string &name);
+  explicit BaseClientProxy(const std::string &name);
   ~BaseClientProxy() override = default;
 
   //! @name manipulators
diff --git a/src/lib/server/Config.h b/src/lib/server/Config.h
index 3c7a6dd3d..1d9c4ee65 100644
--- a/src/lib/server/Config.h
+++ b/src/lib/server/Config.h
@@ -201,7 +201,7 @@ public:
     internal_const_iterator m_i;
   };
 
-  Config(IEventQueue *events);
+  explicit Config(IEventQueue *events);
   virtual ~Config() = default;
 
   //! @name manipulators
diff --git a/src/lib/server/InputFilter.h b/src/lib/server/InputFilter.h
index a2cdfaa73..71aff127f 100644
--- a/src/lib/server/InputFilter.h
+++ b/src/lib/server/InputFilter.h
@@ -301,7 +301,7 @@ public:
   {
   public:
     Rule();
-    Rule(Condition *adopted);
+    explicit Rule(Condition *adopted);
     Rule(const Rule &);
     ~Rule();
 
@@ -355,7 +355,7 @@ public:
   // -------------------------------------------------------------------------
   using RuleList = std::vector<Rule>;
 
-  InputFilter(IEventQueue *events);
+  explicit InputFilter(IEventQueue *events);
   InputFilter(const InputFilter &);
   virtual ~InputFilter();
 
diff --git a/src/lib/server/Server.h b/src/lib/server/Server.h
index 207cd1b6e..1e959175a 100644
--- a/src/lib/server/Server.h
+++ b/src/lib/server/Server.h
@@ -86,8 +86,9 @@ public:
   class ScreenConnectedInfo
   {
   public:
-    ScreenConnectedInfo(std::string screen) : m_screen(screen)
+    explicit ScreenConnectedInfo(std::string screen) : m_screen(screen)
     {
+      // do nothing
     }
 
   public: