diff --git a/rtengine/curves.h b/rtengine/curves.h
index deed5d0fe..98ce68015 100644
--- a/rtengine/curves.h
+++ b/rtengine/curves.h
@@ -468,7 +468,7 @@ protected:
     void NURBS_set ();
 
 public:
-    DiagonalCurve (const std::vector<double>& points, int ppn = CURVES_MIN_POLY_POINTS);
+    explicit DiagonalCurve (const std::vector<double>& points, int ppn = CURVES_MIN_POLY_POINTS);
     ~DiagonalCurve () override;
 
     double getVal     (double t) const override;
@@ -493,7 +493,7 @@ private:
 
 public:
 
-    FlatCurve (const std::vector<double>& points, bool isPeriodic = true, int ppn = CURVES_MIN_POLY_POINTS);
+    explicit FlatCurve (const std::vector<double>& points, bool isPeriodic = true, int ppn = CURVES_MIN_POLY_POINTS);
     ~FlatCurve () override;
 
     double getVal     (double t) const override;
diff --git a/rtengine/imagedata.h b/rtengine/imagedata.h
index d06820296..774547487 100644
--- a/rtengine/imagedata.h
+++ b/rtengine/imagedata.h
@@ -98,7 +98,7 @@ private:
     unsigned int dcrawFrameCount;
 
 public:
-    FramesData (const Glib::ustring& fname, std::unique_ptr<RawMetaDataLocation> rml = nullptr, bool firstFrameOnly = false);
+    explicit FramesData (const Glib::ustring& fname, std::unique_ptr<RawMetaDataLocation> rml = nullptr, bool firstFrameOnly = false);
     ~FramesData () override;
 
     void setDCRawFrameCount (unsigned int frameCount);
diff --git a/rtengine/improcfun.h b/rtengine/improcfun.h
index cd1650f6e..d3e6f4032 100644
--- a/rtengine/improcfun.h
+++ b/rtengine/improcfun.h
@@ -200,7 +200,7 @@ public:
 
     double lumimul[3];
 
-    ImProcFunctions(const ProcParams* iparams, bool imultiThread = true)
+    explicit ImProcFunctions(const ProcParams* iparams, bool imultiThread = true)
         : monitorTransform(nullptr), params(iparams), scale(1), multiThread(imultiThread), lumimul{} {}
     ~ImProcFunctions();
     bool needsLuminanceOnly()
diff --git a/rtengine/procparams.h b/rtengine/procparams.h
index 46eb530bc..369af85fa 100644
--- a/rtengine/procparams.h
+++ b/rtengine/procparams.h
@@ -1634,8 +1634,8 @@ class PartialProfile :
 {
 public:
     PartialProfile(bool createInstance = false, bool paramsEditedValue = false);
-    PartialProfile(ProcParams* pp, ParamsEdited* pe = nullptr, bool fullCopy = false);
-    PartialProfile(const ProcParams* pp, const ParamsEdited* pe = nullptr);
+    explicit PartialProfile(ProcParams* pp, ParamsEdited* pe = nullptr, bool fullCopy = false);
+    explicit PartialProfile(const ProcParams* pp, const ParamsEdited* pe = nullptr);
     void deleteInstance();
     void clearGeneral();
     int  load(const Glib::ustring& fName);
diff --git a/rtgui/curveeditorgroup.h b/rtgui/curveeditorgroup.h
index 80a1a95a4..ae0ebee07 100644
--- a/rtgui/curveeditorgroup.h
+++ b/rtgui/curveeditorgroup.h
@@ -70,7 +70,7 @@ public:
      *                 dialogs.
      */
 
-    CurveEditorGroup(Glib::ustring& curveDir, Glib::ustring groupLabel = "");
+    explicit CurveEditorGroup(Glib::ustring& curveDir, Glib::ustring groupLabel = "");
     ~CurveEditorGroup() override;
     void newLine();
     void curveListComplete();
diff --git a/rtgui/guiutils.h b/rtgui/guiutils.h
index e4c38f347..73cd27171 100644
--- a/rtgui/guiutils.h
+++ b/rtgui/guiutils.h
@@ -400,7 +400,7 @@ protected:
     void set_none();
 
 public:
-    MyFileChooserButton(const Glib::ustring &title, Gtk::FileChooserAction action=Gtk::FILE_CHOOSER_ACTION_OPEN);
+    explicit MyFileChooserButton(const Glib::ustring &title, Gtk::FileChooserAction action=Gtk::FILE_CHOOSER_ACTION_OPEN);
 
     sigc::signal<void> &signal_selection_changed();
     sigc::signal<void> &signal_file_set();
diff --git a/rtgui/popupcommon.h b/rtgui/popupcommon.h
index f939dbe96..92d6a6214 100644
--- a/rtgui/popupcommon.h
+++ b/rtgui/popupcommon.h
@@ -47,7 +47,7 @@ public:
     type_signal_item_selected signal_item_selected();
     Gtk::Grid* buttonGroup;    // this is the widget to be packed
 
-    PopUpCommon (Gtk::Button* button, const Glib::ustring& label = "");
+    explicit PopUpCommon (Gtk::Button* button, const Glib::ustring& label = "");
     virtual ~PopUpCommon ();
     bool addEntry (const Glib::ustring& fileName, const Glib::ustring& label);
     int getEntryCount () const;
diff --git a/rtgui/rtimage.h b/rtgui/rtimage.h
index 5679f6edc..244d0030a 100644
--- a/rtgui/rtimage.h
+++ b/rtgui/rtimage.h
@@ -38,11 +38,11 @@ protected:
 public:
     RTImage ();
     RTImage (RTImage &other);
-    RTImage (Glib::RefPtr<Gdk::Pixbuf> &pixbuf);
-    RTImage (Cairo::RefPtr<Cairo::ImageSurface> &surf);
-    RTImage(Cairo::RefPtr<Cairo::ImageSurface> other);
-    RTImage (Glib::RefPtr<RTImage> &other);
-    RTImage (const Glib::ustring& fileName, const Glib::ustring& rtlFileName = Glib::ustring());
+    explicit RTImage (Glib::RefPtr<Gdk::Pixbuf> &pixbuf);
+    explicit RTImage (Cairo::RefPtr<Cairo::ImageSurface> &surf);
+    explicit RTImage(Cairo::RefPtr<Cairo::ImageSurface> other);
+    explicit RTImage (Glib::RefPtr<RTImage> &other);
+    explicit RTImage (const Glib::ustring& fileName, const Glib::ustring& rtlFileName = Glib::ustring());
 
     void setImage (const Glib::ustring& fileName, const Glib::ustring& rtlFileName = Glib::ustring());
     void changeImage (const Glib::ustring& imageName);
diff --git a/rtgui/rtsurface.h b/rtgui/rtsurface.h
index c314ab1c1..b442b7493 100644
--- a/rtgui/rtsurface.h
+++ b/rtgui/rtsurface.h
@@ -30,7 +30,7 @@ class RTSurface :
 {
 public:
     RTSurface();
-    RTSurface(const Glib::ustring& fileName, const Glib::ustring& rtlFileName = {});
+    explicit RTSurface(const Glib::ustring& fileName, const Glib::ustring& rtlFileName = {});
 
     void setImage(const Glib::ustring& fileName, const Glib::ustring& rtlFileName = {});