diff --git a/eth/main.cpp b/eth/main.cpp
index 2d79f4954..15041d651 100644
--- a/eth/main.cpp
+++ b/eth/main.cpp
@@ -612,6 +612,7 @@ int main(int argc, char** argv)
 		else if (arg == "--opencl-device" && i + 1 < argc)
 			try {
 				openclDevice = stol(argv[++i]);
+				miningThreads = 1;
 			}
 			catch (...)
 			{
diff --git a/libethash-cl/ethash_cl_miner.cpp b/libethash-cl/ethash_cl_miner.cpp
index 891d3f97d..111f92529 100644
--- a/libethash-cl/ethash_cl_miner.cpp
+++ b/libethash-cl/ethash_cl_miner.cpp
@@ -24,6 +24,7 @@
 
 #include <cstdio>
 #include <cstdlib>
+#include <iostream>
 #include <assert.h>
 #include <queue>
 #include <vector>
@@ -43,6 +44,8 @@
 #undef min
 #undef max
 
+using namespace std;
+
 static void add_definition(std::string& source, char const* id, unsigned value)
 {
 	char buf[256];
@@ -63,7 +66,7 @@ std::string ethash_cl_miner::platform_info(unsigned _platformId, unsigned _devic
 	cl::Platform::get(&platforms);
 	if (platforms.empty())
 	{
-		debugf("No OpenCL platforms found.\n");
+		cout << "No OpenCL platforms found." << endl;
 		return std::string();
 	}
 
@@ -73,7 +76,7 @@ std::string ethash_cl_miner::platform_info(unsigned _platformId, unsigned _devic
 	platforms[platform_num].getDevices(CL_DEVICE_TYPE_ALL, &devices);
 	if (devices.empty())
 	{
-		debugf("No OpenCL devices found.\n");
+		cout << "No OpenCL devices found." << endl;
 		return std::string();
 	}
 
@@ -91,7 +94,7 @@ unsigned ethash_cl_miner::get_num_devices(unsigned _platformId)
 	cl::Platform::get(&platforms);
 	if (platforms.empty())
 	{
-		debugf("No OpenCL platforms found.\n");
+		cout << "No OpenCL platforms found." << endl;
 		return 0;
 	}
 
@@ -100,7 +103,7 @@ unsigned ethash_cl_miner::get_num_devices(unsigned _platformId)
 	platforms[platform_num].getDevices(CL_DEVICE_TYPE_ALL, &devices);
 	if (devices.empty())
 	{
-		debugf("No OpenCL devices found.\n");
+		cout << "No OpenCL devices found." << endl;
 		return 0;
 	}
 	return devices.size();
@@ -124,7 +127,7 @@ bool ethash_cl_miner::init(ethash_params const& params, std::function<void(void*
     cl::Platform::get(&platforms);
 	if (platforms.empty())
 	{
-		debugf("No OpenCL platforms found.\n");
+		cout << "No OpenCL platforms found." << endl;
 		return false;
 	}
 
@@ -132,31 +135,25 @@ bool ethash_cl_miner::init(ethash_params const& params, std::function<void(void*
 
 	_platformId = std::min<unsigned>(_platformId, platforms.size() - 1);
 
-	fprintf(stderr, "Using platform: %s\n", platforms[_platformId].getInfo<CL_PLATFORM_NAME>().c_str());
+	cout << "Using platform: " << platforms[_platformId].getInfo<CL_PLATFORM_NAME>().c_str() << endl;
 
     // get GPU device of the default platform
     std::vector<cl::Device> devices;
 	platforms[_platformId].getDevices(CL_DEVICE_TYPE_ALL, &devices);
     if (devices.empty())
 	{
-		debugf("No OpenCL devices found.\n");
+		cout << "No OpenCL devices found." << endl;
 		return false;
 	}
 
-	// use default device
+	// use selected device
 	cl::Device& device = devices[std::min<unsigned>(_deviceId, devices.size() - 1)];
-	for (unsigned n = 0; n < devices.size(); ++n)
-	{
-		auto version = devices[n].getInfo<CL_DEVICE_VERSION>();
-		auto name = devices[n].getInfo<CL_DEVICE_NAME>();
-		fprintf(stderr, "%s %d: %s (%s)\n", n == _deviceId ? "USING " : "      ", n, name.c_str(), version.c_str());
-	}
 	std::string device_version = device.getInfo<CL_DEVICE_VERSION>();
-	fprintf(stderr, "Using device: %s (%s)\n", device.getInfo<CL_DEVICE_NAME>().c_str(),device_version.c_str());
+	cout << "Using device: " << device.getInfo<CL_DEVICE_NAME>().c_str() << "(" << device_version.c_str() << ")" << endl;
 
 	if (strncmp("OpenCL 1.0", device_version.c_str(), 10) == 0)
 	{
-		debugf("OpenCL 1.0 is not supported.\n");
+		cout << "OpenCL 1.0 is not supported." << endl;
 		return false;
 	}
 	if (strncmp("OpenCL 1.1", device_version.c_str(), 10) == 0)
@@ -190,7 +187,7 @@ bool ethash_cl_miner::init(ethash_params const& params, std::function<void(void*
 	}
 	catch (cl::Error err)
 	{
-		debugf("%s\n", program.getBuildInfo<CL_PROGRAM_BUILD_LOG>(device).c_str());
+		cout << program.getBuildInfo<CL_PROGRAM_BUILD_LOG>(device).c_str();
 		return false;
 	}
 	m_hash_kernel = cl::Kernel(program, "ethash_hash");
diff --git a/libethcore/Ethash.cpp b/libethcore/Ethash.cpp
index c40ce2625..66dc953b7 100644
--- a/libethcore/Ethash.cpp
+++ b/libethcore/Ethash.cpp
@@ -311,7 +311,7 @@ void Ethash::GPUMiner::workLoop()
 
 			auto p = EthashAux::params(m_minerSeed);
 			auto cb = [&](void* d) { EthashAux::full(m_minerSeed, bytesRef((byte*)d, p.full_size)); };
-			unsigned device = instances() > 0 ? index() : s_deviceId;
+			unsigned device = instances() > 1 ? index() : s_deviceId;
 			m_miner->init(p, cb, 32, s_platformId, device);
 		}