diff --git a/distrho/src/DistrhoPluginInternal.hpp b/distrho/src/DistrhoPluginInternal.hpp
index e175f5e8..e42fe867 100644
--- a/distrho/src/DistrhoPluginInternal.hpp
+++ b/distrho/src/DistrhoPluginInternal.hpp
@@ -309,6 +309,9 @@ struct Plugin::PrivateData {
 #if DISTRHO_PLUGIN_WANT_STATE
     bool updateStateValueCallback(const char* const key, const char* const value)
     {
+        DISTRHO_SAFE_ASSERT_RETURN(key != nullptr && key[0] != '\0', false);
+        DISTRHO_SAFE_ASSERT_RETURN(value != nullptr, false);
+
         d_stdout("updateStateValueCallback %p", updateStateValueCallbackFunc);
         if (updateStateValueCallbackFunc != nullptr)
             return updateStateValueCallbackFunc(callbacksPtr, key, value);
diff --git a/distrho/src/DistrhoUI.cpp b/distrho/src/DistrhoUI.cpp
index a8fb9602..d6ee6170 100644
--- a/distrho/src/DistrhoUI.cpp
+++ b/distrho/src/DistrhoUI.cpp
@@ -171,18 +171,18 @@ static double getDesktopScaleFactor(const uintptr_t parentWindowHandle)
 
 UI::PrivateData* UI::PrivateData::s_nextPrivateData = nullptr;
 
-PluginWindow& UI::PrivateData::createNextWindow(UI* const ui, uint width, uint height, const bool adjustForScaleFactor)
+PluginWindow& UI::PrivateData::createNextWindow(UI* const ui, uint width, uint height)
 {
     UI::PrivateData* const uiData = s_nextPrivateData;
     const double scaleFactor = d_isNotZero(uiData->scaleFactor) ? uiData->scaleFactor : getDesktopScaleFactor(uiData->winId);
 
-    if (adjustForScaleFactor && d_isNotZero(scaleFactor) && d_isNotEqual(scaleFactor, 1.0))
+    if (d_isNotZero(scaleFactor) && d_isNotEqual(scaleFactor, 1.0))
     {
         width *= scaleFactor;
         height *= scaleFactor;
     }
 
-    d_stdout("createNextWindow %u %u %f %d", width, height, scaleFactor, adjustForScaleFactor);
+    d_stdout("createNextWindow %u %u %d", width, height, scaleFactor);
     uiData->window = new PluginWindow(ui, uiData->app, uiData->winId, width, height, scaleFactor);
 
     if (uiData->callbacksPtr != nullptr)
@@ -323,13 +323,7 @@ UI::UI(const uint width, const uint height, const bool automaticallyScaleAndSetA
               #ifdef DISTRHO_UI_DEFAULT_HEIGHT
                height == 0 ? DISTRHO_UI_DEFAULT_HEIGHT :
               #endif
-               height,
-               // adjustForScaleFactor
-              #ifdef DISTRHO_UI_DEFAULT_WIDTH
-               width == 0
-              #else
-               false
-              #endif
+               height
                )),
       uiData(UI::PrivateData::s_nextPrivateData)
 {
diff --git a/distrho/src/DistrhoUIPrivateData.hpp b/distrho/src/DistrhoUIPrivateData.hpp
index 03a5b253..bcbcbfcc 100644
--- a/distrho/src/DistrhoUIPrivateData.hpp
+++ b/distrho/src/DistrhoUIPrivateData.hpp
@@ -352,6 +352,9 @@ struct UI::PrivateData {
 
     void setStateCallback(const char* const key, const char* const value)
     {
+        DISTRHO_SAFE_ASSERT_RETURN(key != nullptr && key[0] != '\0',);
+        DISTRHO_SAFE_ASSERT_RETURN(value != nullptr,);
+
         if (setStateCallbackFunc != nullptr)
             setStateCallbackFunc(callbacksPtr, key, value);
     }
@@ -364,6 +367,8 @@ struct UI::PrivateData {
 
     void setSizeCallback(const uint width, const uint height)
     {
+        DISTRHO_SAFE_ASSERT_RETURN(width != 0 && height != 0,);
+
         if (setSizeCallbackFunc != nullptr)
             setSizeCallbackFunc(callbacksPtr, width, height);
     }
@@ -372,7 +377,7 @@ struct UI::PrivateData {
     bool fileRequestCallback(const char* key);
 
     static UI::PrivateData* s_nextPrivateData;
-    static PluginWindow& createNextWindow(UI* ui, uint width, uint height, bool adjustForScaleFactor);
+    static PluginWindow& createNextWindow(UI* ui, uint width, uint height);
    #if DISTRHO_UI_USE_WEB_VIEW
     static void webViewMessageCallback(void* arg, char* msg);
    #endif