diff --git a/distrho/src/DistrhoPluginVST.hpp b/distrho/src/DistrhoPluginVST.hpp
index 7d08adc8..cfdcf111 100644
--- a/distrho/src/DistrhoPluginVST.hpp
+++ b/distrho/src/DistrhoPluginVST.hpp
@@ -67,24 +67,24 @@ START_NAMESPACE_DISTRHO
 // --------------------------------------------------------------------------------------------------------------------
 
 enum Vst3InternalParameters {
-#if DPF_VST3_USES_SEPARATE_CONTROLLER
+   #if DPF_VST3_USES_SEPARATE_CONTROLLER
     kVst3InternalParameterBufferSize,
     kVst3InternalParameterSampleRate,
-#endif
-#if DISTRHO_PLUGIN_WANT_LATENCY
+   #endif
+   #if DISTRHO_PLUGIN_WANT_LATENCY
     kVst3InternalParameterLatency,
-#endif
-#if DISTRHO_PLUGIN_WANT_PROGRAMS
+   #endif
+   #if DISTRHO_PLUGIN_WANT_PROGRAMS
     kVst3InternalParameterProgram,
-#endif
+   #endif
     kVst3InternalParameterBaseCount,
-#if DISTRHO_PLUGIN_WANT_MIDI_INPUT
+   #if DISTRHO_PLUGIN_WANT_MIDI_INPUT
     kVst3InternalParameterMidiCC_start = kVst3InternalParameterBaseCount,
     kVst3InternalParameterMidiCC_end = kVst3InternalParameterMidiCC_start + 130*16,
     kVst3InternalParameterCount = kVst3InternalParameterMidiCC_end
-#else
+   #else
     kVst3InternalParameterCount = kVst3InternalParameterBaseCount
-#endif
+   #endif
 };
 
 #if DPF_VST3_USES_SEPARATE_CONTROLLER || DISTRHO_PLUGIN_WANT_LATENCY || DISTRHO_PLUGIN_WANT_PROGRAMS || DISTRHO_PLUGIN_WANT_MIDI_INPUT
diff --git a/distrho/src/DistrhoPluginVST3.cpp b/distrho/src/DistrhoPluginVST3.cpp
index 6244b7c0..86f2fce9 100644
--- a/distrho/src/DistrhoPluginVST3.cpp
+++ b/distrho/src/DistrhoPluginVST3.cpp
@@ -1095,7 +1095,7 @@ public:
                 if (fPlugin.isParameterOutputOrTrigger(i))
                     continue;
                 fParameterValueChangesForUI[kVst3InternalParameterBaseCount + i] = false;
-                sendParameterSetToUI(kVst3InternalParameterBaseCount + i,
+                sendParameterSetToUI(kVst3InternalParameterCount + i,
                                      fCachedParameterValues[kVst3InternalParameterBaseCount + i]);
             }
         }
@@ -1933,7 +1933,7 @@ public:
             return 0.0;
        #endif
 
-       #if DPF_VST3_USES_SEPARATE_CONTROLLER || DISTRHO_PLUGIN_WANT_LATENCY || DISTRHO_PLUGIN_WANT_PROGRAMS
+      #if DPF_VST3_HAS_INTERNAL_PARAMETERS && !DPF_VST3_PURE_MIDI_INTERNAL_PARAMETERS
         switch (rindex)
         {
        #if DPF_VST3_USES_SEPARATE_CONTROLLER
@@ -1948,7 +1948,7 @@ public:
        #endif
             return plainParameterToNormalized(rindex, fCachedParameterValues[rindex]);
         }
-       #endif
+      #endif
 
         const uint32_t index = static_cast<uint32_t>(rindex - kVst3InternalParameterCount);
         DISTRHO_SAFE_ASSERT_UINT2_RETURN(index < fParameterCount, index, fParameterCount, 0.0);
@@ -2002,7 +2002,7 @@ public:
                 {
                     if (fPlugin.isParameterOutputOrTrigger(i))
                         continue;
-                    fCachedParameterValues[kVst3InternalParameterCount + i] = fPlugin.getParameterValue(i);
+                    fCachedParameterValues[kVst3InternalParameterBaseCount + i] = fPlugin.getParameterValue(i);
                 }
 
                #if DISTRHO_PLUGIN_HAS_UI
@@ -2019,6 +2019,8 @@ public:
         }
        #endif
 
+        DISTRHO_SAFE_ASSERT_UINT2_RETURN(rindex >= kVst3InternalParameterCount, rindex, kVst3InternalParameterCount, V3_INVALID_ARG);
+
        #if DPF_VST3_USES_SEPARATE_CONTROLLER
         const uint32_t index = static_cast<uint32_t>(rindex - kVst3InternalParameterCount);
         DISTRHO_SAFE_ASSERT_UINT2_RETURN(index < fParameterCount, index, fParameterCount, V3_INVALID_ARG);
@@ -2026,11 +2028,6 @@ public:
         setNormalizedPluginParameterValue(index, normalized);
        #endif
         return V3_OK;
-
-       #if !DPF_VST3_HAS_INTERNAL_PARAMETERS
-        // unused
-        (void)rindex;
-       #endif
     }
 
     v3_result setComponentHandler(v3_component_handler** const handler) noexcept
@@ -2139,7 +2136,7 @@ public:
             for (uint32_t i=0; i<fParameterCount; ++i)
             {
                 fParameterValueChangesForUI[kVst3InternalParameterBaseCount + i] = false;
-                sendParameterSetToUI(kVst3InternalParameterBaseCount + i,
+                sendParameterSetToUI(kVst3InternalParameterCount + i,
                                      fCachedParameterValues[kVst3InternalParameterBaseCount + i]);
             }
 
@@ -2177,7 +2174,7 @@ public:
                     continue;
 
                 fParameterValueChangesForUI[kVst3InternalParameterBaseCount + i] = false;
-                sendParameterSetToUI(kVst3InternalParameterBaseCount + i,
+                sendParameterSetToUI(kVst3InternalParameterCount + i,
                                      fCachedParameterValues[kVst3InternalParameterBaseCount + i]);
             }
 
diff --git a/distrho/src/DistrhoUIVST3.cpp b/distrho/src/DistrhoUIVST3.cpp
index eba6ec6f..75d7ed1f 100644
--- a/distrho/src/DistrhoUIVST3.cpp
+++ b/distrho/src/DistrhoUIVST3.cpp
@@ -556,10 +556,13 @@ public:
                #endif
                 }
 
+                // others like latency and buffer-size do not matter on UI side
                 return V3_OK;
             }
 
-            const uint32_t index = static_cast<uint32_t>(rindex) - kVst3InternalParameterBaseCount;
+            DISTRHO_SAFE_ASSERT_UINT2_RETURN(rindex >= kVst3InternalParameterCount, rindex, kVst3InternalParameterCount, V3_INVALID_ARG);
+            const uint32_t index = static_cast<uint32_t>(rindex - kVst3InternalParameterCount);
+
             fUI.parameterChanged(index, value);
             return V3_OK;
         }