diff --git a/src/engine/engine.cpp b/src/engine/engine.cpp
index 320425c7f..e96005405 100644
--- a/src/engine/engine.cpp
+++ b/src/engine/engine.cpp
@@ -1594,6 +1594,7 @@ void DivEngine::unmuteAll() {
 }
 
 int DivEngine::addInstrument(int refChan) {
+  if (song.ins.size()>=256) return -1;
   BUSY_BEGIN;
   DivInstrument* ins=new DivInstrument;
   int insCount=(int)song.ins.size();
@@ -1624,6 +1625,10 @@ int DivEngine::addInstrument(int refChan) {
 }
 
 int DivEngine::addInstrumentPtr(DivInstrument* which) {
+  if (song.ins.size()>=256) {
+    delete which;
+    return -1;
+  }
   BUSY_BEGIN;
   saveLock.lock();
   song.ins.push_back(which);
@@ -1668,6 +1673,7 @@ void DivEngine::delInstrument(int index) {
 }
 
 int DivEngine::addWave() {
+  if (song.wave.size()>=256) return -1;
   BUSY_BEGIN;
   saveLock.lock();
   DivWavetable* wave=new DivWavetable;
@@ -1680,37 +1686,48 @@ int DivEngine::addWave() {
 }
 
 bool DivEngine::addWaveFromFile(const char* path) {
+  if (song.wave.size()>=256) {
+    lastError="too many wavetables!";
+    return false;
+  }
   FILE* f=ps_fopen(path,"rb");
   if (f==NULL) {
+    lastError=fmt::sprintf("%s",strerror(errno));
     return false;
   }
   unsigned char* buf;
   ssize_t len;
   if (fseek(f,0,SEEK_END)!=0) {
     fclose(f);
+    lastError=fmt::sprintf("could not seek to end: %s",strerror(errno));
     return false;
   }
   len=ftell(f);
   if (len<0) {
     fclose(f);
+    lastError=fmt::sprintf("could not determine file size: %s",strerror(errno));
     return false;
   }
   if (len==(SIZE_MAX>>1)) {
     fclose(f);
+    lastError="file size is invalid!";
     return false;
   }
   if (len==0) {
     fclose(f);
+    lastError="file is empty";
     return false;
   }
   if (fseek(f,0,SEEK_SET)!=0) {
     fclose(f);
+    lastError=fmt::sprintf("could not seek to beginning: %s",strerror(errno));
     return false;
   }
   buf=new unsigned char[len];
   if (fread(buf,1,len,f)!=(size_t)len) {
     logW("did not read entire wavetable file buffer!");
     delete[] buf;
+    lastError=fmt::sprintf("could not read entire file: %s",strerror(errno));
     return false;
   }
   fclose(f);
@@ -1790,6 +1807,7 @@ bool DivEngine::addWaveFromFile(const char* path) {
   } catch (EndOfFileException& e) {
     delete wave;
     delete[] buf;
+    lastError="premature end of file";
     return false;
   }
   
@@ -1816,6 +1834,7 @@ void DivEngine::delWave(int index) {
 }
 
 int DivEngine::addSample() {
+  if (song.sample.size()>=256) return -1;
   BUSY_BEGIN;
   saveLock.lock();
   DivSample* sample=new DivSample;
@@ -1830,6 +1849,10 @@ int DivEngine::addSample() {
 }
 
 int DivEngine::addSampleFromFile(const char* path) {
+  if (song.sample.size()>=256) {
+    lastError="too many samples!";
+    return -1;
+  }
   BUSY_BEGIN;
   warnings="";
 
diff --git a/src/gui/doAction.cpp b/src/gui/doAction.cpp
index 2e1dd3779..8a71d9a38 100644
--- a/src/gui/doAction.cpp
+++ b/src/gui/doAction.cpp
@@ -525,14 +525,22 @@ void FurnaceGUI::doAction(int what) {
 
     case GUI_ACTION_INS_LIST_ADD:
       curIns=e->addInstrument(cursor.xCoarse);
-      MARK_MODIFIED;
+      if (curIns==-1) {
+        showError("too many instruments!");
+      } else {
+        MARK_MODIFIED;
+      }
       break;
     case GUI_ACTION_INS_LIST_DUPLICATE:
       if (curIns>=0 && curIns<(int)e->song.ins.size()) {
         int prevIns=curIns;
         curIns=e->addInstrument(cursor.xCoarse);
-        (*e->song.ins[curIns])=(*e->song.ins[prevIns]);
-        MARK_MODIFIED;
+        if (curIns==-1) {
+          showError("too many instruments!");
+        } else {
+          (*e->song.ins[curIns])=(*e->song.ins[prevIns]);
+          MARK_MODIFIED;
+        }
       }
       break;
     case GUI_ACTION_INS_LIST_OPEN:
@@ -571,14 +579,22 @@ void FurnaceGUI::doAction(int what) {
     
     case GUI_ACTION_WAVE_LIST_ADD:
       curWave=e->addWave();
-      MARK_MODIFIED;
+      if (curWave==-1) {
+        showError("too many wavetables!");
+      } else {
+        MARK_MODIFIED;
+      }
       break;
     case GUI_ACTION_WAVE_LIST_DUPLICATE:
       if (curWave>=0 && curWave<(int)e->song.wave.size()) {
         int prevWave=curWave;
         curWave=e->addWave();
-        (*e->song.wave[curWave])=(*e->song.wave[prevWave]);
-        MARK_MODIFIED;
+        if (curWave==-1) {
+          showError("too many wavetables!");
+        } else {
+          (*e->song.wave[curWave])=(*e->song.wave[prevWave]);
+          MARK_MODIFIED;
+        }
       }
       break;
     case GUI_ACTION_WAVE_LIST_OPEN:
@@ -614,31 +630,39 @@ void FurnaceGUI::doAction(int what) {
 
     case GUI_ACTION_SAMPLE_LIST_ADD:
       curSample=e->addSample();
+      if (curSample==-1) {
+        showError("too many samples!");
+      } else {
+        MARK_MODIFIED;
+      }
       updateSampleTex=true;
-      MARK_MODIFIED;
       break;
     case GUI_ACTION_SAMPLE_LIST_DUPLICATE:
       if (curSample>=0 && curSample<(int)e->song.sample.size()) {
         DivSample* prevSample=e->getSample(curSample);
         curSample=e->addSample();
-        updateSampleTex=true;
-        e->lockEngine([this,prevSample]() {
-          DivSample* sample=e->getSample(curSample);
-          if (sample!=NULL) {
-            sample->rate=prevSample->rate;
-            sample->centerRate=prevSample->centerRate;
-            sample->name=prevSample->name;
-            sample->loopStart=prevSample->loopStart;
-            sample->depth=prevSample->depth;
-            if (sample->init(prevSample->samples)) {
-              if (prevSample->getCurBuf()!=NULL) {
-                memcpy(sample->getCurBuf(),prevSample->getCurBuf(),prevSample->getCurBufLen());
+        if (curSample==-1) {
+          showError("too many samples!");
+        } else {
+          e->lockEngine([this,prevSample]() {
+            DivSample* sample=e->getSample(curSample);
+            if (sample!=NULL) {
+              sample->rate=prevSample->rate;
+              sample->centerRate=prevSample->centerRate;
+              sample->name=prevSample->name;
+              sample->loopStart=prevSample->loopStart;
+              sample->depth=prevSample->depth;
+              if (sample->init(prevSample->samples)) {
+                if (prevSample->getCurBuf()!=NULL) {
+                  memcpy(sample->getCurBuf(),prevSample->getCurBuf(),prevSample->getCurBufLen());
+                }
               }
             }
-          }
-          e->renderSamples();
-        });
-        MARK_MODIFIED;
+            e->renderSamples();
+          });
+          MARK_MODIFIED;
+        }
+        updateSampleTex=true;
       }
       break;
     case GUI_ACTION_SAMPLE_LIST_OPEN:
@@ -1154,11 +1178,15 @@ void FurnaceGUI::doAction(int what) {
       if (curSample<0 || curSample>=(int)e->song.sample.size()) break;
       DivSample* sample=e->song.sample[curSample];
       curIns=e->addInstrument(cursor.xCoarse);
-      e->song.ins[curIns]->type=DIV_INS_AMIGA;
-      e->song.ins[curIns]->name=sample->name;
-      e->song.ins[curIns]->amiga.initSample=curSample;
-      nextWindow=GUI_WINDOW_INS_EDIT;
-      MARK_MODIFIED;
+      if (curIns==-1) {
+        showError("too many instruments!");
+      } else {
+        e->song.ins[curIns]->type=DIV_INS_AMIGA;
+        e->song.ins[curIns]->name=sample->name;
+        e->song.ins[curIns]->amiga.initSample=curSample;
+        nextWindow=GUI_WINDOW_INS_EDIT;
+        MARK_MODIFIED;
+      }
       break;
     }
 
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index c52809b05..00f0da2b3 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -3161,8 +3161,11 @@ bool FurnaceGUI::loop() {
               break;
             }
             case GUI_FILE_WAVE_OPEN:
-              e->addWaveFromFile(copyOfName.c_str());
-              MARK_MODIFIED;
+              if (!e->addWaveFromFile(copyOfName.c_str())) {
+                showError("cannot load wavetable! ("+e->getLastError()+")");
+              } else {
+                MARK_MODIFIED;
+              }
               break;
             case GUI_FILE_EXPORT_VGM: {
               SafeWriter* w=e->saveVGM(willExport,vgmExportLoop,vgmExportVersion);