diff --git a/scripting/abc.cpp b/scripting/abc.cpp
index 4a7d9d53c3..0beda4c8dd 100644
--- a/scripting/abc.cpp
+++ b/scripting/abc.cpp
@@ -2055,7 +2055,7 @@ ASObject* method_info::getOptional(unsigned int i) const
 BlockStudy* method_info::mergeBlocks(uint32_t aggregateStart, uint32_t aggregateEnd)
 {
 	auto itStart=lower_bound(studiedBlocks.begin(),studiedBlocks.end(),aggregateStart);
-	auto itEnd=lower_bound(studiedBlocks.begin(),studiedBlocks.end(),aggregateEnd-1)-1;
+	auto itEnd=upper_bound(studiedBlocks.begin(),studiedBlocks.end(),aggregateEnd-1)-1;
 	assert(itStart!=studiedBlocks.end());
 	assert(itStart->start<=aggregateStart && itStart->end>aggregateStart);
 	assert(itEnd->start<=aggregateEnd && itEnd->end>=aggregateEnd);
@@ -2085,7 +2085,7 @@ BlockStudy* method_info::getBlockStudyAtAddress(uint32_t ip, CREATE_STUDY_BLOCK
 			if(createBlock==CREATE)
 			{
 				it->usageCount++;
-				if(it->compiledCode==NULL && it->usageCount>usageCountThreshold)
+				if(it->blockType==BlockStudy::JIT_CANDIDATE && it->usageCount>usageCountThreshold)
 				{
 					//This block is a candidate for compilation
 					uint32_t aggregateStart=it->start;
@@ -2130,6 +2130,7 @@ BlockStudy* method_info::getBlockStudyAtAddress(uint32_t ip, CREATE_STUDY_BLOCK
 					if(it->start!=aggregateStart || it->end!=aggregateEnd)
 						b=mergeBlocks(aggregateStart, aggregateEnd);
 					b->compiledCode=compileBlock(b->start,b->end);
+					b->blockType=(b->compiledCode)?(BlockStudy::JIT_OK):(BlockStudy::JIT_FAILED);
 				}
 			}
 			return b;
@@ -2139,29 +2140,6 @@ BlockStudy* method_info::getBlockStudyAtAddress(uint32_t ip, CREATE_STUDY_BLOCK
 		return NULL;
 	afterIt=studiedBlocks.insert(afterIt, BlockStudy(ip));
 	return &(*afterIt);
-
-/*	//TODO: optimize the search
-	for(uint32_t i=0;i<studiedBlocks.size();i++)
-	{
-		assert(studiedBlocks[i].start<studiedBlocks[i].end);
-		if(studiedBlocks[i].isAddressInside(ip))
-		{
-			if(createBlock==CREATE)
-			{
-				studiedBlocks[i].usageCount++;
-				if(studiedBlocks[i].compiledCode==NULL &&
-					studiedBlocks[i].usageCount>usageCountThreshold)
-				{
-					studiedBlocks[i].compiledCode=compileBlock(studiedBlocks[i].start,studiedBlocks[i].end);
-				}
-			}
-			return &studiedBlocks[i];
-		}
-	}
-	if(createBlock==DO_NOT_CREATE)
-		return NULL;
-	studiedBlocks.emplace_back(ip);
-	return &studiedBlocks.back();*/
 }
 
 istream& lightspark::operator>>(istream& in, u32& v)
diff --git a/scripting/abc.h b/scripting/abc.h
index 833f4dea7a..bf3d49596c 100644
--- a/scripting/abc.h
+++ b/scripting/abc.h
@@ -221,12 +221,16 @@ inline stack_entry make_stack_entry(llvm::Value* v, STACK_TYPE t)
 struct BlockStudy
 {
 	//start is the first address inside the block
+	uint32_t start;
 	//end is the first byte _not_ inside the block
-	uint32_t start,end;
+	uint32_t end;
 	uint32_t usageCount;
+
+	enum BLOCK_TYPE { JIT_CANDIDATE=0, JIT_OK, JIT_FAILED };
+	BLOCK_TYPE blockType;
 	typedef intptr_t (*synt_block)(call_context* cc);
 	synt_block compiledCode;
-	BlockStudy(uint32_t a):start(a),end(a+1),usageCount(1),compiledCode(NULL)
+	BlockStudy(uint32_t a):start(a),end(a+1),usageCount(1),blockType(JIT_CANDIDATE),compiledCode(NULL)
 	{
 	}
 	bool isAddressInside(uint32_t ip) const
diff --git a/scripting/abc_codesynt.cpp b/scripting/abc_codesynt.cpp
index e71faa1e59..034d9204dc 100644
--- a/scripting/abc_codesynt.cpp
+++ b/scripting/abc_codesynt.cpp
@@ -2383,6 +2383,8 @@ BlockStudy::synt_block method_info::compileBlock(uint32_t start, uint32_t end)
 			default:
 				LOG(LOG_ERROR,_("Not implemented instruction @") << code.tellg());
 				LOG(LOG_ERROR,_("Opcode ") << hex << (unsigned int)opcode << dec);
+				llvmf->eraseFromParent();
+				cout << "Failed to compile " << profName << endl;
 				return NULL;
 				/*constant = llvm::ConstantInt::get(int_type, opcode);
 				Builder.CreateCall(ex->FindFunctionNamed("not_impl"), constant);
@@ -2464,8 +2466,7 @@ BlockStudy::synt_block method_info::compileBlock(uint32_t start, uint32_t end)
 		}
 	}
 
-	//__asm__("int $3");
-	cout << "start: " << start << " end: " << end << endl;
+	//cout << profName << " start: " << start << " end: " << end << endl;
 	//llvmf->dump();
 	getVm()->FPM->run(*llvmf);
 	BlockStudy::synt_block ret=(BlockStudy::synt_block)getVm()->ex->getPointerToFunction(llvmf);
diff --git a/scripting/abc_interpreter.cpp b/scripting/abc_interpreter.cpp
index cfdc68d066..d753fcc12c 100644
--- a/scripting/abc_interpreter.cpp
+++ b/scripting/abc_interpreter.cpp
@@ -73,7 +73,7 @@ ASObject* ABCVm::executeFunction(SyntheticFunction* function, call_context* cont
 		if(mi->studyFunction)
 		{
 			BlockStudy* nextBlock=mi->getBlockStudyAtAddress(instructionPointer, method_info::DO_NOT_CREATE);
-			if(nextBlock && nextBlock->compiledCode && nextBlock->start==instructionPointer)
+			if(nextBlock && nextBlock->blockType==BlockStudy::JIT_OK && nextBlock->start==instructionPointer)
 			{
 				//Call JItted code
 				mi->checkJITAssumptions(context);
diff --git a/scripting/toplevel.cpp b/scripting/toplevel.cpp
index 754dc3f916..01b6ea938c 100644
--- a/scripting/toplevel.cpp
+++ b/scripting/toplevel.cpp
@@ -2244,8 +2244,8 @@ ASObject* SyntheticFunction::call(ASObject* obj, ASObject* const* args, uint32_t
 		return NULL;
 	}
 
-	if(mi->profName=="BigInteger::http://crypto.hurlant.com/BigInteger::am" && mi->studyFunction==false)
-//	if(hit_count==hit_threshold)
+//	if(mi->profName=="BigInteger::http://crypto.hurlant.com/BigInteger::am" && mi->studyFunction==false)
+	if(hit_count==hit_threshold)
 	{
 		cout << "Studying " << mi->profName << endl;
 		mi->studyFunction=true;