diff --git a/testable-agent/src/main/java/com/alibaba/testable/agent/handler/SourceClassHandler.java b/testable-agent/src/main/java/com/alibaba/testable/agent/handler/SourceClassHandler.java
index e54d7c7..fa72454 100644
--- a/testable-agent/src/main/java/com/alibaba/testable/agent/handler/SourceClassHandler.java
+++ b/testable-agent/src/main/java/com/alibaba/testable/agent/handler/SourceClassHandler.java
@@ -122,21 +122,17 @@ public class SourceClassHandler extends BaseClassHandler {
         for (int i = rangeEnd - 1; i >= 0; i--) {
             switch (instructions[i].getOpcode()) {
                 case Opcodes.INVOKESPECIAL:
-                    stackLevel += ClassUtil.getParameterTypes(((MethodInsnNode)instructions[i]).desc).size();
+                case Opcodes.INVOKEVIRTUAL:
+                case Opcodes.INVOKEINTERFACE:
+                    stackLevel += stackEffectOfInvocation(instructions[i]) + 1;
                     if (((MethodInsnNode)instructions[i]).name.equals(ConstPool.CONSTRUCTOR)) {
-                        // constructor implicitly eat 2 more stack and return 1 value
+                        // constructor must be INVOKESPECIAL and implicitly pop 1 more stack
                         stackLevel++;
                     }
                     break;
                 case Opcodes.INVOKESTATIC:
                 case Opcodes.INVOKEDYNAMIC:
-                    // static and dynamic invoke implicitly return 1 value
-                    stackLevel += (ClassUtil.getParameterTypes(((MethodInsnNode)instructions[i]).desc).size() - 1);
-                    break;
-                case Opcodes.INVOKEVIRTUAL:
-                case Opcodes.INVOKEINTERFACE:
-                    // virtual and interface invoke implicitly eat 1 more stack and return 1 value, deuce
-                    stackLevel += ClassUtil.getParameterTypes(((MethodInsnNode)instructions[i]).desc).size();
+                    stackLevel += stackEffectOfInvocation(instructions[i]);
                     break;
                 case -1:
                     // reach LineNumberNode or LabelNode
@@ -151,6 +147,11 @@ public class SourceClassHandler extends BaseClassHandler {
         return -1;
     }
 
+    private int stackEffectOfInvocation(AbstractInsnNode instruction) {
+        String desc = ((MethodInsnNode)instruction).desc;
+        return ClassUtil.getParameterTypes(desc).size() - (ClassUtil.getReturnType(desc).isEmpty() ? 0 : 1);
+    }
+
     private AbstractInsnNode[] replaceNewOps(ClassNode cn, MethodNode mn, String newOperatorInjectMethodName,
                                              AbstractInsnNode[] instructions, int start, int end) {
         LogUtil.debug("  Using %s mock new operation in %s", newOperatorInjectMethodName, mn.name);
diff --git a/testable-agent/src/main/java/com/alibaba/testable/agent/util/ClassUtil.java b/testable-agent/src/main/java/com/alibaba/testable/agent/util/ClassUtil.java
index f8e311f..5b1cd48 100644
--- a/testable-agent/src/main/java/com/alibaba/testable/agent/util/ClassUtil.java
+++ b/testable-agent/src/main/java/com/alibaba/testable/agent/util/ClassUtil.java
@@ -26,6 +26,7 @@ public class ClassUtil {
     public static final byte TYPE_CLASS = 'L';
     public static final byte TYPE_SHORT = 'S';
     public static final byte TYPE_BOOL = 'Z';
+    public static final byte TYPE_VOID = 'V';
     private static final byte PARAM_END = ')';
     private static final byte CLASS_END = ';';
     private static final byte TYPE_ARRAY = '[';
@@ -39,6 +40,7 @@ public class ClassUtil {
     private static final String CLASS_LONG = "java/lang/Long";
     private static final String CLASS_SHORT = "java/lang/Short";
     private static final String CLASS_BOOLEAN = "java/lang/Boolean";
+    private static final String EMPTY = "";
     private static final String METHOD_VALUE_OF = "valueOf";
 
     private final static String JOINER = "::";
@@ -56,6 +58,7 @@ public class ClassUtil {
         TYPE_MAPPING.put(TYPE_LONG, CLASS_LONG);
         TYPE_MAPPING.put(TYPE_SHORT, CLASS_SHORT);
         TYPE_MAPPING.put(TYPE_BOOL, CLASS_BOOLEAN);
+        TYPE_MAPPING.put(TYPE_VOID, EMPTY);
     }
 
     /**
@@ -159,7 +162,7 @@ public class ClassUtil {
         } else if (TYPE_MAPPING.containsKey((byte)typeChar)) {
             return TYPE_MAPPING.get((byte)typeChar);
         } else {
-            return "";
+            return EMPTY;
         }
     }