diff --git a/CMakeLists_files.cmake b/CMakeLists_files.cmake
index bf893d36c..abe322fdc 100644
--- a/CMakeLists_files.cmake
+++ b/CMakeLists_files.cmake
@@ -62,6 +62,7 @@ list (APPEND MAIN_SOURCE_FILES
   opm/models/blackoil/blackoilpolymerparams.cpp
   opm/models/blackoil/blackoilsolventparams.cpp
   opm/models/parallel/mpiutil.cpp
+  opm/models/parallel/tasklets.cpp
   opm/models/parallel/threadmanager.cpp
   opm/simulators/flow/ActionHandler.cpp
   opm/simulators/flow/Banners.cpp
diff --git a/opm/models/parallel/tasklets.cpp b/opm/models/parallel/tasklets.cpp
new file mode 100644
index 000000000..390edacfd
--- /dev/null
+++ b/opm/models/parallel/tasklets.cpp
@@ -0,0 +1,205 @@
+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 2 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+
+  Consult the COPYING file in the top-level source directory of this
+  module for the precise wording of the license and the list of
+  copyright holders.
+*/
+#include <config.h>
+#include <opm/models/parallel/tasklets.hpp>
+
+#include <atomic>
+#include <condition_variable>
+#include <iostream>
+#include <mutex>
+#include <queue>
+#include <stdexcept>
+#include <thread>
+
+namespace Opm {
+
+thread_local TaskletRunner* TaskletRunner::taskletRunner_ = nullptr;
+thread_local int TaskletRunner::workerThreadIndex_ = -1;
+
+TaskletRunner::BarrierTasklet::BarrierTasklet(unsigned numWorkers)
+    : TaskletInterface(/*refCount=*/numWorkers)
+{
+    numWorkers_ = numWorkers;
+    numWaiting_ = 0;
+}
+
+void TaskletRunner::BarrierTasklet::run()
+{
+    wait();
+}
+
+void TaskletRunner::BarrierTasklet::wait()
+{
+    std::unique_lock<std::mutex> lock(barrierMutex_);
+
+    numWaiting_ += 1;
+    if (numWaiting_ >= numWorkers_ + 1) {
+        lock.unlock();
+        barrierCondition_.notify_all();
+    }
+    else {
+        const auto& areAllWaiting =
+            [this]() -> bool
+            { return this->numWaiting_ >= this->numWorkers_ + 1; };
+
+        barrierCondition_.wait(lock, /*predicate=*/areAllWaiting);
+    }
+}
+
+TaskletRunner::TaskletRunner(unsigned numWorkers)
+{
+    threads_.resize(numWorkers);
+    for (unsigned i = 0; i < numWorkers; ++i)
+        // create a worker thread
+        threads_[i].reset(new std::thread(startWorkerThread_, this, i));
+}
+
+TaskletRunner::~TaskletRunner()
+{
+    if (threads_.size() > 0) {
+        // dispatch a tasklet which will terminate the worker thread
+        dispatch(std::make_shared<TerminateThreadTasklet>());
+
+        // wait until all worker threads have terminated
+        for (auto& thread : threads_)
+            thread->join();
+    }
+}
+
+bool TaskletRunner::failure() const
+{
+    return this->failureFlag_.load(std::memory_order_relaxed);
+}
+
+int TaskletRunner::workerThreadIndex() const
+{
+    if (TaskletRunner::taskletRunner_ != this)
+        return -1;
+    return TaskletRunner::workerThreadIndex_;
+}
+
+void TaskletRunner::dispatch(std::shared_ptr<TaskletInterface> tasklet)
+{
+    if (threads_.empty()) {
+        // run the tasklet immediately in synchronous mode.
+        while (tasklet->referenceCount() > 0) {
+            tasklet->dereference();
+            try {
+                tasklet->run();
+            }
+            catch (const std::exception& e) {
+                std::cerr << "ERROR: Uncaught std::exception when running tasklet: " << e.what() << ". Trying to continue.\n";
+                failureFlag_.store(true, std::memory_order_relaxed);
+            }
+            catch (...) {
+                std::cerr << "ERROR: Uncaught exception (general type) when running tasklet. Trying to continue.\n";
+                failureFlag_.store(true, std::memory_order_relaxed);
+            }
+        }
+    }
+    else {
+        // lock mutex for the tasklet queue to make sure that nobody messes with the
+        // task queue
+        taskletQueueMutex_.lock();
+
+        // add the tasklet to the queue
+        taskletQueue_.push(tasklet);
+
+        taskletQueueMutex_.unlock();
+
+        workAvailableCondition_.notify_all();
+    }
+}
+
+void TaskletRunner::barrier()
+{
+    unsigned numWorkers = threads_.size();
+    if (numWorkers == 0)
+        // nothing needs to be done to implement a barrier in synchronous mode
+        return;
+
+    // dispatch a barrier tasklet and wait until it has been run by the worker thread
+    auto barrierTasklet = std::make_shared<BarrierTasklet>(numWorkers);
+    dispatch(barrierTasklet);
+
+    barrierTasklet->wait();
+}
+
+void TaskletRunner::startWorkerThread_(TaskletRunner* taskletRunner, int workerThreadIndex)
+{
+    TaskletRunner::taskletRunner_ = taskletRunner;
+    TaskletRunner::workerThreadIndex_ = workerThreadIndex;
+
+    taskletRunner->run_();
+}
+
+void TaskletRunner::run_()
+{
+    while (true) {
+
+        // wait until tasklets have been pushed to the queue. first we need to lock
+        // mutex for access to taskletQueue_
+        std::unique_lock<std::mutex> lock(taskletQueueMutex_);
+
+        const auto& workIsAvailable =
+            [this]() -> bool
+            { return !taskletQueue_.empty(); };
+
+        if (!workIsAvailable())
+            workAvailableCondition_.wait(lock, /*predicate=*/workIsAvailable);
+
+        // remove tasklet from queue
+        std::shared_ptr<TaskletInterface> tasklet = taskletQueue_.front();
+
+        // if tasklet is an end marker, terminate the thread and DO NOT remove the
+        // tasklet.
+        if (tasklet->isEndMarker()) {
+            if(taskletQueue_.size() > 1)
+                throw std::logic_error("TaskletRunner: Not all queued tasklets were executed");
+            taskletQueueMutex_.unlock();
+            return;
+        }
+
+        tasklet->dereference();
+        if (tasklet->referenceCount() == 0)
+            // remove tasklets from the queue as soon as their reference count
+            // reaches zero, i.e. the tasklet has been run often enough.
+            taskletQueue_.pop();
+        lock.unlock();
+
+        // execute tasklet
+        try {
+            tasklet->run();
+        }
+        catch (const std::exception& e) {
+            std::cerr << "ERROR: Uncaught std::exception when running tasklet: " << e.what() << ".\n";
+            failureFlag_.store(true, std::memory_order_relaxed);
+        }
+        catch (...) {
+            std::cerr << "ERROR: Uncaught exception when running tasklet.\n";
+            failureFlag_.store(true, std::memory_order_relaxed);
+        }
+    }
+}
+
+} // end namespace Opm
diff --git a/opm/models/parallel/tasklets.hpp b/opm/models/parallel/tasklets.hpp
index 0e783c45b..8a952a327 100644
--- a/opm/models/parallel/tasklets.hpp
+++ b/opm/models/parallel/tasklets.hpp
@@ -28,12 +28,9 @@
 #define OPM_TASKLETS_HPP
 
 #include <atomic>
-#include <stdexcept>
-#include <cassert>
 #include <thread>
 #include <queue>
 #include <mutex>
-#include <iostream>
 #include <condition_variable>
 
 namespace Opm {
@@ -83,25 +80,6 @@ private:
     const Fn& fn_;
 };
 
-class TaskletRunner;
-
-// this class stores the thread local static attributes for the TaskletRunner class. we
-// cannot put them directly into TaskletRunner because defining static members for
-// non-template classes in headers leads the linker to choke in case multiple compile
-// units are used.
-template <class Dummy = void>
-struct TaskletRunnerHelper_
-{
-    static thread_local TaskletRunner* taskletRunner_;
-    static thread_local int workerThreadIndex_;
-};
-
-template <class Dummy>
-thread_local TaskletRunner* TaskletRunnerHelper_<Dummy>::taskletRunner_ = nullptr;
-
-template <class Dummy>
-thread_local int TaskletRunnerHelper_<Dummy>::workerThreadIndex_ = -1;
-
 /*!
  * \brief Handles where a given tasklet is run.
  *
@@ -114,33 +92,11 @@ class TaskletRunner
     class BarrierTasklet : public TaskletInterface
     {
     public:
-        BarrierTasklet(unsigned numWorkers)
-            : TaskletInterface(/*refCount=*/numWorkers)
-        {
-            numWorkers_ = numWorkers;
-            numWaiting_ = 0;
-        }
+        BarrierTasklet(unsigned numWorkers);
 
-        void run()
-        { wait(); }
+        void run();
 
-        void wait()
-        {
-            std::unique_lock<std::mutex> lock(barrierMutex_);
-
-            numWaiting_ += 1;
-            if (numWaiting_ >= numWorkers_ + 1) {
-                lock.unlock();
-                barrierCondition_.notify_all();
-            }
-            else {
-                const auto& areAllWaiting =
-                    [this]() -> bool
-                    { return this->numWaiting_ >= this->numWorkers_ + 1; };
-
-                barrierCondition_.wait(lock, /*predicate=*/areAllWaiting);
-            }
-        }
+        void wait();
 
     private:
         unsigned numWorkers_;
@@ -172,13 +128,7 @@ public:
      * The number of worker threads may be 0. In this case, all work is done by the main
      * thread (synchronous mode).
      */
-    TaskletRunner(unsigned numWorkers)
-    {
-        threads_.resize(numWorkers);
-        for (unsigned i = 0; i < numWorkers; ++i)
-            // create a worker thread
-            threads_[i].reset(new std::thread(startWorkerThread_, this, i));
-    }
+    TaskletRunner(unsigned numWorkers);
 
     /*!
      * \brief Destructor
@@ -187,34 +137,16 @@ public:
      * worker threads have been terminated, i.e. all scheduled tasklets are guaranteed to
      * be completed.
      */
-    ~TaskletRunner()
-    {
-        if (threads_.size() > 0) {
-            // dispatch a tasklet which will terminate the worker thread
-            dispatch(std::make_shared<TerminateThreadTasklet>());
+    ~TaskletRunner();
 
-            // wait until all worker threads have terminated
-            for (auto& thread : threads_)
-                thread->join();
-        }
-    }
-
-    bool failure() const
-    {
-        return this->failureFlag_.load(std::memory_order_relaxed);
-    }
+    bool failure() const;
 
     /*!
      * \brief Returns the index of the current worker thread.
      *
      * If the current thread is not a worker thread, -1 is returned.
      */
-    int workerThreadIndex() const
-    {
-        if (TaskletRunnerHelper_<void>::taskletRunner_ != this)
-            return -1;
-        return TaskletRunnerHelper_<void>::workerThreadIndex_;
-    }
+    int workerThreadIndex() const;
 
     /*!
      * \brief Returns the number of worker threads for the tasklet runner.
@@ -227,38 +159,7 @@ public:
      *
      * The tasklet is either run immediately or deferred to a separate thread.
      */
-    void dispatch(std::shared_ptr<TaskletInterface> tasklet)
-    {
-        if (threads_.empty()) {
-            // run the tasklet immediately in synchronous mode.
-            while (tasklet->referenceCount() > 0) {
-                tasklet->dereference();
-                try {
-                    tasklet->run();
-                }
-                catch (const std::exception& e) {
-                    std::cerr << "ERROR: Uncaught std::exception when running tasklet: " << e.what() << ". Trying to continue.\n";
-                    failureFlag_.store(true, std::memory_order_relaxed);
-                }
-                catch (...) {
-                    std::cerr << "ERROR: Uncaught exception (general type) when running tasklet. Trying to continue.\n";
-                    failureFlag_.store(true, std::memory_order_relaxed);
-                }
-            }
-        }
-        else {
-            // lock mutex for the tasklet queue to make sure that nobody messes with the
-            // task queue
-            taskletQueueMutex_.lock();
-
-            // add the tasklet to the queue
-            taskletQueue_.push(tasklet);
-
-            taskletQueueMutex_.unlock();
-
-            workAvailableCondition_.notify_all();
-        }
-    }
+    void dispatch(std::shared_ptr<TaskletInterface> tasklet);
 
     /*!
      * \brief Convenience method to construct a new function runner tasklet and dispatch it immediately.
@@ -275,19 +176,8 @@ public:
     /*!
      * \brief Make sure that all tasklets have been completed after this method has been called
      */
-    void barrier()
-    {
-        unsigned numWorkers = threads_.size();
-        if (numWorkers == 0)
-            // nothing needs to be done to implement a barrier in synchronous mode
-            return;
+    void barrier();
 
-        // dispatch a barrier tasklet and wait until it has been run by the worker thread
-        auto barrierTasklet = std::make_shared<BarrierTasklet>(numWorkers);
-        dispatch(barrierTasklet);
-
-        barrierTasklet->wait();
-    }
 private:
     // Atomic flag that is set to failure if any of the tasklets run by the TaskletRunner fails.
     // This flag is checked before new tasklets run or get dispatched and in case it is true, the
@@ -301,68 +191,18 @@ private:
 
 protected:
     // main function of the worker thread
-    static void startWorkerThread_(TaskletRunner* taskletRunner, int workerThreadIndex)
-    {
-        TaskletRunnerHelper_<void>::taskletRunner_ = taskletRunner;
-        TaskletRunnerHelper_<void>::workerThreadIndex_ = workerThreadIndex;
-
-        taskletRunner->run_();
-    }
+    static void startWorkerThread_(TaskletRunner* taskletRunner, int workerThreadIndex);
 
     //! do the work until the queue received an end tasklet
-    void run_()
-    {
-        while (true) {
-
-            // wait until tasklets have been pushed to the queue. first we need to lock
-            // mutex for access to taskletQueue_
-            std::unique_lock<std::mutex> lock(taskletQueueMutex_);
-
-            const auto& workIsAvailable =
-                [this]() -> bool
-                { return !taskletQueue_.empty(); };
-
-            if (!workIsAvailable())
-                workAvailableCondition_.wait(lock, /*predicate=*/workIsAvailable);
-
-            // remove tasklet from queue
-            std::shared_ptr<TaskletInterface> tasklet = taskletQueue_.front();
-
-            // if tasklet is an end marker, terminate the thread and DO NOT remove the
-            // tasklet.
-            if (tasklet->isEndMarker()) {
-                if(taskletQueue_.size() > 1)
-                    throw std::logic_error("TaskletRunner: Not all queued tasklets were executed");
-                taskletQueueMutex_.unlock();
-                return;
-            }
-
-            tasklet->dereference();
-            if (tasklet->referenceCount() == 0)
-                // remove tasklets from the queue as soon as their reference count
-                // reaches zero, i.e. the tasklet has been run often enough.
-                taskletQueue_.pop();
-            lock.unlock();
-
-            // execute tasklet
-            try {
-                tasklet->run();
-            }
-            catch (const std::exception& e) {
-                std::cerr << "ERROR: Uncaught std::exception when running tasklet: " << e.what() << ".\n";
-                failureFlag_.store(true, std::memory_order_relaxed); 
-            }
-            catch (...) {
-                std::cerr << "ERROR: Uncaught exception when running tasklet.\n";
-                failureFlag_.store(true, std::memory_order_relaxed);
-            }
-        }
-    }
+    void run_();
 
     std::vector<std::unique_ptr<std::thread> > threads_;
     std::queue<std::shared_ptr<TaskletInterface> > taskletQueue_;
     std::mutex taskletQueueMutex_;
     std::condition_variable workAvailableCondition_;
+
+    static thread_local TaskletRunner* taskletRunner_;
+    static thread_local int workerThreadIndex_;
 };
 
 } // end namespace Opm
diff --git a/tests/models/test_tasklets.cpp b/tests/models/test_tasklets.cpp
index a95db6eba..838f7fccc 100644
--- a/tests/models/test_tasklets.cpp
+++ b/tests/models/test_tasklets.cpp
@@ -30,6 +30,7 @@
 
 #include <opm/models/parallel/tasklets.hpp>
 
+#include <cassert>
 #include <chrono>
 #include <iostream>