diff --git a/dgl/EventHandlers.hpp b/dgl/EventHandlers.hpp
index dddeb427..a460440e 100644
--- a/dgl/EventHandlers.hpp
+++ b/dgl/EventHandlers.hpp
@@ -52,7 +52,7 @@ public:
     };
 
     explicit ButtonEventHandler(SubWidget* self);
-    ~ButtonEventHandler();
+    virtual ~ButtonEventHandler();
 
     bool isActive() noexcept;
     void setActive(bool active, bool sendCallback) noexcept;
@@ -117,7 +117,7 @@ public:
     explicit KnobEventHandler(SubWidget* self);
     explicit KnobEventHandler(SubWidget* self, const KnobEventHandler& other);
     KnobEventHandler& operator=(const KnobEventHandler& other);
-    ~KnobEventHandler();
+    virtual ~KnobEventHandler();
 
     // returns raw value, is assumed to be scaled if using log
     float getValue() const noexcept;
@@ -154,6 +154,15 @@ private:
     struct PrivateData;
     PrivateData* const pData;
 
+    /* not for use */
+#ifdef DISTRHO_PROPER_CPP11_SUPPORT
+    KnobEventHandler(KnobEventHandler& other) = delete;
+    KnobEventHandler(const KnobEventHandler& other) = delete;
+#else
+    KnobEventHandler(KnobEventHandler& other);
+    KnobEventHandler(const KnobEventHandler& other);
+#endif
+
     DISTRHO_LEAK_DETECTOR(KnobEventHandler)
 };
 
diff --git a/dgl/NanoVG.hpp b/dgl/NanoVG.hpp
index 08b8f50b..4a8fd52c 100644
--- a/dgl/NanoVG.hpp
+++ b/dgl/NanoVG.hpp
@@ -23,6 +23,10 @@
 #include "TopLevelWidget.hpp"
 #include "StandaloneWindow.hpp"
 
+#ifdef _MSC_VER
+# pragma warning(disable:4661) /* instantiated template classes whose methods are defined elsewhere */
+#endif
+
 #ifndef DGL_NO_SHARED_RESOURCES
 # define NANOVG_DEJAVU_SANS_TTF "__dpf_dejavusans_ttf__"
 #endif
@@ -964,4 +968,8 @@ typedef NanoSubWidget NanoWidget;
 
 END_NAMESPACE_DGL
 
+#ifdef _MSC_VER
+# pragma warning(enable:4661)
+#endif
+
 #endif // DGL_NANO_WIDGET_HPP_INCLUDED
diff --git a/dgl/src/Color.cpp b/dgl/src/Color.cpp
index 4aa6b45d..10382fbd 100644
--- a/dgl/src/Color.cpp
+++ b/dgl/src/Color.cpp
@@ -114,10 +114,10 @@ Color::Color(const Color& color1, const Color& color2, const float u) noexcept
     interpolate(color2, u);
 }
 
-Color Color::withAlpha(const float alpha) noexcept
+Color Color::withAlpha(const float alpha2) noexcept
 {
     Color color(*this);
-    color.alpha = alpha;
+    color.alpha = alpha2;
     return color;
 }
 
diff --git a/dgl/src/Geometry.cpp b/dgl/src/Geometry.cpp
index 44e99185..eb8df6e5 100644
--- a/dgl/src/Geometry.cpp
+++ b/dgl/src/Geometry.cpp
@@ -1,6 +1,6 @@
 /*
  * DISTRHO Plugin Framework (DPF)
- * Copyright (C) 2012-2019 Filipe Coelho <falktx@falktx.com>
+ * Copyright (C) 2012-2021 Filipe Coelho <falktx@falktx.com>
  *
  * Permission to use, copy, modify, and/or distribute this software for any purpose with
  * or without fee is hereby granted, provided that the above copyright notice and this
@@ -15,8 +15,10 @@
  */
 
 #ifdef _MSC_VER
-// instantiated template classes whose methods are defined elsewhere
-# pragma warning(disable:4661)
+# pragma warning(disable:4661) /* instantiated template classes whose methods are defined elsewhere */
+#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
 #endif
 
 #include "../Geometry.hpp"
diff --git a/dgl/src/OpenGL.cpp b/dgl/src/OpenGL.cpp
index aa2c3960..eb619c3a 100644
--- a/dgl/src/OpenGL.cpp
+++ b/dgl/src/OpenGL.cpp
@@ -678,7 +678,7 @@ void Window::PrivateData::renderToPicture(const char* const filename,
     GLubyte* const pixels = new GLubyte[width * height * 3 * sizeof(GLubyte)];
 
     glFlush();
-    glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels);
+    glReadPixels(0, 0, static_cast<GLsizei>(width), static_cast<GLsizei>(height), GL_RGB, GL_UNSIGNED_BYTE, pixels);
 
     fprintf(f, "P3\n%d %d\n255\n", width, height);
     for (uint y = 0; y < height; y++)
diff --git a/dgl/src/SubWidget.cpp b/dgl/src/SubWidget.cpp
index c4cfd0b8..32c93221 100644
--- a/dgl/src/SubWidget.cpp
+++ b/dgl/src/SubWidget.cpp
@@ -34,7 +34,9 @@ SubWidget::~SubWidget()
 template<typename T>
 bool SubWidget::contains(const T x, const T y) const noexcept
 {
-    return Rectangle<double>(0, 0, getWidth()-pData->margin.getX(), getHeight()-pData->margin.getY()).contains(x, y);
+    return Rectangle<double>(0, 0,
+                             static_cast<double>(getWidth()) - pData->margin.getX(),
+                             static_cast<double>(getHeight()) - pData->margin.getY()).contains(x, y);
 }
 
 template<typename T>
diff --git a/dgl/src/Window.cpp b/dgl/src/Window.cpp
index 7d27613c..c9d12df7 100644
--- a/dgl/src/Window.cpp
+++ b/dgl/src/Window.cpp
@@ -220,10 +220,10 @@ void Window::setSize(uint width, uint height)
             {
                 // fix width
                 if (reqRatio > ratio)
-                    width = height * ratio;
+                    width = static_cast<uint>(height * ratio + 0.5);
                 // fix height
                 else
-                    height = width / ratio;
+                    height = static_cast<uint>(static_cast<double>(width) / ratio + 0.5);
             }
         }
     }
diff --git a/distrho/src/DistrhoPluginInternal.hpp b/distrho/src/DistrhoPluginInternal.hpp
index 011936a6..af82b84e 100644
--- a/distrho/src/DistrhoPluginInternal.hpp
+++ b/distrho/src/DistrhoPluginInternal.hpp
@@ -355,7 +355,7 @@ public:
 
             portGroupIndices.erase(kPortGroupNone);
 
-            if (const size_t portGroupSize = portGroupIndices.size())
+            if (const uint32_t portGroupSize = portGroupIndices.size())
             {
                 fData->portGroups = new PortGroupWithId[portGroupSize];
                 fData->portGroupCount = portGroupSize;