diff --git a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationBuilder.java b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationBuilder.java
index 8c7d8df98..bc8baaa99 100644
--- a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationBuilder.java
+++ b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationBuilder.java
@@ -39,6 +39,7 @@ public class DebugInformationBuilder implements DebugInformationEmitter {
         return locationProvider;
     }
 
+    @Override
     public void setLocationProvider(LocationProvider locationProvider) {
         this.locationProvider = locationProvider;
     }
@@ -114,8 +115,9 @@ public class DebugInformationBuilder implements DebugInformationEmitter {
                 fileDesc.methodMap = fileDescProto.methodMap.toArray(new MethodReference[0]);
                 fileDesc.generatedLocations = new GeneratedLocation[fileDescProto.generatedLocations.size()][];
                 for (int i = 0; i < fileDescProto.generatedLocations.size(); ++i) {
-                    fileDesc.generatedLocations[i] = fileDescProto.generatedLocations.get(index)
-                            .toArray(new GeneratedLocation[0]);
+                    List<GeneratedLocation> locations = fileDescProto.generatedLocations.get(index);
+                    fileDesc.generatedLocations[i] = locations != null ?
+                            locations.toArray(new GeneratedLocation[0]) : null;
                 }
             }
         }
@@ -132,6 +134,10 @@ public class DebugInformationBuilder implements DebugInformationEmitter {
                         line - generatedLocations.size() + 1, null));
             }
             List<GeneratedLocation> existingLocations = generatedLocations.get(line);
+            if (existingLocations == null) {
+                existingLocations = new ArrayList<>();
+                generatedLocations.set(line, existingLocations);
+            }
             existingLocations.add(location);
         }
 
diff --git a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationEmitter.java b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationEmitter.java
index c22a846a4..df2d3f678 100644
--- a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationEmitter.java
+++ b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationEmitter.java
@@ -15,6 +15,7 @@
  */
 package org.teavm.debugging;
 
+import org.teavm.codegen.LocationProvider;
 import org.teavm.model.MethodReference;
 
 /**
@@ -22,6 +23,8 @@ import org.teavm.model.MethodReference;
  * @author Alexey Andreev
  */
 public interface DebugInformationEmitter {
+    void setLocationProvider(LocationProvider locationProvider);
+
     void emitLocation(String fileName, int line);
 
     void emitMethod(MethodReference method);
diff --git a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationWriter.java b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationWriter.java
index f6abcc6da..f4b83a6db 100644
--- a/teavm-core/src/main/java/org/teavm/debugging/DebugInformationWriter.java
+++ b/teavm-core/src/main/java/org/teavm/debugging/DebugInformationWriter.java
@@ -110,7 +110,11 @@ class DebugInformationWriter {
 
     private void writeNumber(int number) throws IOException {
         do {
-            number = (number << 1) | (number >>> 31);
+            if (number < 0) {
+                number = (-number << 1) | 1;
+            } else {
+                number = number << 1;
+            }
             byte b = (byte)(number & 0x7F);
             if ((number & 0xFFFFFF80) != 0) {
                 b |= 0x80;
diff --git a/teavm-core/src/main/java/org/teavm/debugging/DummyDebugInformationEmitter.java b/teavm-core/src/main/java/org/teavm/debugging/DummyDebugInformationEmitter.java
index 38cff54b4..1bfa50782 100644
--- a/teavm-core/src/main/java/org/teavm/debugging/DummyDebugInformationEmitter.java
+++ b/teavm-core/src/main/java/org/teavm/debugging/DummyDebugInformationEmitter.java
@@ -15,6 +15,7 @@
  */
 package org.teavm.debugging;
 
+import org.teavm.codegen.LocationProvider;
 import org.teavm.model.MethodReference;
 
 
@@ -30,4 +31,8 @@ public class DummyDebugInformationEmitter implements DebugInformationEmitter {
     @Override
     public void emitMethod(MethodReference method) {
     }
+
+    @Override
+    public void setLocationProvider(LocationProvider locationProvider) {
+    }
 }
diff --git a/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java b/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
index 065dd1a81..a7e186502 100644
--- a/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
+++ b/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
@@ -232,7 +232,7 @@ public class Decompiler {
                 InstructionLocation lastLocation = null;
                 NodeLocation nodeLocation = null;
                 for (Instruction insn : generator.currentBlock.getInstructions()) {
-                    if (lastLocation != insn.getLocation()) {
+                    if (insn.getLocation() != null && lastLocation != insn.getLocation()) {
                         lastLocation = insn.getLocation();
                         nodeLocation = new NodeLocation(lastLocation.getFileName(), lastLocation.getLine());
                     }
diff --git a/teavm-core/src/main/java/org/teavm/model/BasicBlock.java b/teavm-core/src/main/java/org/teavm/model/BasicBlock.java
index 62d493133..1ada9dc84 100644
--- a/teavm-core/src/main/java/org/teavm/model/BasicBlock.java
+++ b/teavm-core/src/main/java/org/teavm/model/BasicBlock.java
@@ -172,7 +172,11 @@ public class BasicBlock implements BasicBlockReader {
 
     @Override
     public void readInstruction(int index, InstructionReader reader) {
-        instructions.get(index).acceptVisitor(new InstructionReadVisitor(reader));
+        Instruction insn = instructions.get(index);
+        if (insn.getLocation() != null) {
+            reader.location(insn.getLocation());
+        }
+        insn.acceptVisitor(new InstructionReadVisitor(reader));
     }
 
     @Override
diff --git a/teavm-core/src/main/java/org/teavm/model/util/InstructionStringifier.java b/teavm-core/src/main/java/org/teavm/model/util/InstructionStringifier.java
index be6d17556..f32559396 100644
--- a/teavm-core/src/main/java/org/teavm/model/util/InstructionStringifier.java
+++ b/teavm-core/src/main/java/org/teavm/model/util/InstructionStringifier.java
@@ -37,8 +37,6 @@ public class InstructionStringifier implements InstructionReader {
             if (location != null) {
                 sb.append("at " + (location.getFileName() != null ? location.getFileName() : "<unknown>") + ":" +
                         (location.getLine() >= 0 ? String.valueOf(location.getLine()) : "<unknown>"));
-            } else {
-                sb.append("<unkwnown>");
             }
             this.location = location;
         }
diff --git a/teavm-core/src/main/java/org/teavm/vm/TeaVM.java b/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
index 24e0570e7..cad245984 100644
--- a/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
+++ b/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
@@ -351,6 +351,7 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
         if (debugEmitter != null) {
             renderer.setDebugEmitter(debugEmitter);
         }
+        debugEmitter.setLocationProvider(sourceWriter);
         for (Map.Entry<MethodReference, Injector> entry : methodInjectors.entrySet()) {
             renderer.addInjector(entry.getKey(), entry.getValue());
         }