diff --git a/porosity/porosity/Contract.cpp b/porosity/porosity/Contract.cpp
index 94a6c9d..26f8492 100644
--- a/porosity/porosity/Contract.cpp
+++ b/porosity/porosity/Contract.cpp
@@ -375,19 +375,29 @@ Contract::walkAndConnectNodes(
     //
     uint32_t next = _block;
     while (true) {
-        auto block = m_listbasicBlockInfo.find(next);
+        auto block = m_listbasicBlockInfo.find(next); // getBlockAt()
         if (block == m_listbasicBlockInfo.end()) break;
+
+        if (block->second.walkedNode) break;
+
         next = block->second.dstDefault;
 
+        // printf("hash = 0x%x, block = 0x%x, default = 0x%x, JUMPI = 0x%x\n", _hash, _block, block->second.dstDefault, block->second.dstJUMPI);
         if (block->second.dstJUMPI) {
+            block->second.walkedNode = true;
             walkAndConnectNodes(_hash, block->second.dstJUMPI);
         }
 
         if (!next) break;
         if (next == NODE_DEADEND) {
-            auto exitNode = m_exitNodesByHash.find(_hash);
-            block->second.dstDefault = exitNode->second;
-            block->second.nextDefault = getBlockAt(block->second.dstDefault);
+            auto exitNode = m_exitNodesByHash.find(_hash); // getBlockAt()
+            if (exitNode != m_exitNodesByHash.end()) {
+                block->second.dstDefault = exitNode->second;
+            }
+
+            if (!block->second.nextDefault) {
+                block->second.nextDefault = getBlockAt(block->second.dstDefault);
+            }
             break; // next
         }
     }
diff --git a/porosity/porosity/Instruction.cpp b/porosity/porosity/Instruction.cpp
index ee14812..66d461c 100644
--- a/porosity/porosity/Instruction.cpp
+++ b/porosity/porosity/Instruction.cpp
@@ -189,6 +189,10 @@ void dev::eth::eachInstruction(
         size_t additional = 0;
         if (isValidInstruction(instr))
             additional = instructionInfo(instr).additional;
+        else {
+            // printf("Invalid instruction. Aborting...\n");
+            return;
+        }
 
         uint32_t offset = std::distance(_mem.begin(), it);
         u256 data;
diff --git a/porosity/porosity/PorosityDefs.h b/porosity/porosity/PorosityDefs.h
index 60b71ee..d4e9256 100644
--- a/porosity/porosity/PorosityDefs.h
+++ b/porosity/porosity/PorosityDefs.h
@@ -160,6 +160,7 @@ typedef struct _BasicBlockInfo
     string name;
 
     bool visited;
+    bool walkedNode;
     u256 dominators;
 
     ConditionAttribute condAttr;