diff --git a/GPU/Common/GPUCommonDefAPI.h b/GPU/Common/GPUCommonDefAPI.h
index febe2dbd0ad0d..c028acc7020a3 100644
--- a/GPU/Common/GPUCommonDefAPI.h
+++ b/GPU/Common/GPUCommonDefAPI.h
@@ -173,7 +173,7 @@
   #define GPUdouble() float
   #define GPUbarrier() threadgroup_barrier(mem_flags::mem_device | mem_flags::mem_threadgroup)
   #define GPUbarrierWarp() simdgroup_barrier(mem_flags::mem_device | mem_flags::mem_threadgroup)
-  #define GPUAtomic(type) atomic<type>                      // atomic variable type
+  #define GPUAtomic(type) type                      // atomic variable type
 #elif defined(__HIPCC__) //Defines for HIP
   #define GPUd() __device__
   #define GPUdDefault() __device__
diff --git a/GPU/Common/GPUCommonMath.h b/GPU/Common/GPUCommonMath.h
index c6681ed03677c..f2daf30842663 100644
--- a/GPU/Common/GPUCommonMath.h
+++ b/GPU/Common/GPUCommonMath.h
@@ -489,6 +489,25 @@ GPUhdi() constexpr int32_t GPUCommonMath::Abs<int32_t>(int32_t x)
   return GPUCA_CHOICE(abs(x), abs(x), abs(x));
 }
 
+#ifdef __METAL__
+// The counters these operate on are plain integers in the transferred structures,
+// as they are for CUDA and HIP. MSL's atomic operations want metal::atomic, which
+// has the same size and alignment. The overload is picked by address space, and a
+// threadgroup pointer has to keep its own: casting one to a device atomic is an
+// error while the qualifier is visible, but a generic pointer resolves here to
+// device and the cast then goes through silently.
+template <class T>
+GPUdi() threadgroup metal::atomic<T>* GPUCommonMathMetalAtomic(threadgroup T* p)
+{
+  return reinterpret_cast<threadgroup metal::atomic<T>*>(p);
+}
+template <class T>
+GPUdi() device metal::atomic<T>* GPUCommonMathMetalAtomic(T* p)
+{
+  return (device metal::atomic<T>*)p;
+}
+#endif
+
 template <class S, class T>
 GPUdi() uint32_t GPUCommonMath::AtomicExchInternal(S* addr, T val)
 {
@@ -499,7 +518,7 @@ GPUdi() uint32_t GPUCommonMath::AtomicExchInternal(S* addr, T val)
 #elif defined(GPUCA_GPUCODE) && (defined(__CUDACC__) || defined(__HIPCC__))
   return ::atomicExch(addr, val);
 #elif defined(GPUCA_GPUCODE) && defined(__METAL__)
-  return atomic_exchange_explicit(addr, val, memory_order_relaxed);
+  return atomic_exchange_explicit(GPUCommonMathMetalAtomic(addr), val, memory_order_relaxed);
 #elif defined(WITH_OPENMP)
   uint32_t old;
   __atomic_exchange(addr, &val, &old, __ATOMIC_SEQ_CST);
@@ -519,7 +538,7 @@ GPUdi() bool GPUCommonMath::AtomicCASInternal(S* addr, T cmp, T val)
 #elif defined(GPUCA_GPUCODE) && (defined(__CUDACC__) || defined(__HIPCC__))
   return ::atomicCAS(addr, cmp, val) == cmp;
 #elif defined(GPUCA_GPUCODE) && defined(__METAL__)
-  return atomic_compare_exchange_weak_explicit(addr, &cmp, val, memory_order_relaxed, memory_order_relaxed);
+  return atomic_compare_exchange_weak_explicit(GPUCommonMathMetalAtomic(addr), &cmp, val, memory_order_relaxed, memory_order_relaxed);
 #elif defined(WITH_OPENMP)
   return __atomic_compare_exchange(addr, &cmp, &val, true, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
 #else
@@ -537,7 +556,7 @@ GPUdi() uint32_t GPUCommonMath::AtomicAddInternal(S* addr, T val)
 #elif defined(GPUCA_GPUCODE) && (defined(__CUDACC__) || defined(__HIPCC__))
   return ::atomicAdd(addr, val);
 #elif defined(GPUCA_GPUCODE) && defined(__METAL__)
-  return atomic_fetch_add_explicit(addr, val, memory_order_relaxed);
+  return atomic_fetch_add_explicit(GPUCommonMathMetalAtomic(addr), val, memory_order_relaxed);
 #elif defined(WITH_OPENMP)
   return __atomic_add_fetch(addr, val, __ATOMIC_SEQ_CST) - val;
 #else
@@ -555,7 +574,7 @@ GPUdi() void GPUCommonMath::AtomicMaxInternal(S* addr, T val)
 #elif defined(GPUCA_GPUCODE) && (defined(__CUDACC__) || defined(__HIPCC__))
   ::atomicMax(addr, val);
 #elif defined(GPUCA_GPUCODE) && defined(__METAL__)
-  atomic_fetch_max_explicit(addr, val, memory_order_relaxed);
+  atomic_fetch_max_explicit(GPUCommonMathMetalAtomic(addr), val, memory_order_relaxed);
 #else
   S current;
   while ((current = *(volatile S*)addr) < val && !AtomicCASInternal(addr, current, val)) {
@@ -573,7 +592,7 @@ GPUdi() void GPUCommonMath::AtomicMinInternal(S* addr, T val)
 #elif defined(GPUCA_GPUCODE) && (defined(__CUDACC__) || defined(__HIPCC__))
   ::atomicMin(addr, val);
 #elif defined(GPUCA_GPUCODE) && defined(__METAL__)
-  atomic_fetch_min_explicit(addr, val, memory_order_relaxed);
+  atomic_fetch_min_explicit(GPUCommonMathMetalAtomic(addr), val, memory_order_relaxed);
 #else
   S current;
   while ((current = *(volatile S*)addr) > val && !AtomicCASInternal(addr, current, val)) {
diff --git a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
index 86fe293a99bfe..cd1b9b32494fd 100644
--- a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
+++ b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
@@ -37,12 +37,12 @@ using namespace o2::tpc::constants;
 // ===========================================================================
 
 template <>
-GPUdii() void GPUTPCCFDecodeZS::Thread<GPUTPCCFDecodeZS::decodeZS>(int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, GPUSharedMemory& smem, processorType& clusterer, int32_t firstHBF, int32_t tpcTimeBinCut)
+GPUdii() void GPUTPCCFDecodeZS::Thread<GPUTPCCFDecodeZS::decodeZS>(int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, GPUsharedref() GPUSharedMemory& smem, processorType& clusterer, int32_t firstHBF, int32_t tpcTimeBinCut)
 {
   GPUTPCCFDecodeZS::decode(clusterer, smem, nBlocks, nThreads, iBlock, iThread, firstHBF, tpcTimeBinCut);
 }
 
-GPUdii() void GPUTPCCFDecodeZS::decode(GPUTPCClusterFinder& clusterer, GPUSharedMemory& s, int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, int32_t firstHBF, int32_t tpcTimeBinCut)
+GPUdii() void GPUTPCCFDecodeZS::decode(GPUTPCClusterFinder& clusterer, GPUsharedref() GPUSharedMemory& s, int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, int32_t firstHBF, int32_t tpcTimeBinCut)
 {
   const uint32_t sector = clusterer.mISector;
 #ifdef GPUCA_GPUCODE
diff --git a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.h b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.h
index 21d4ec0a28958..eed5e0d6f30ac 100644
--- a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.h
+++ b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.h
@@ -45,7 +45,7 @@ class GPUTPCCFDecodeZS : public GPUKernelTemplate
     decodeZS,
   };
 
-  static GPUd() void decode(GPUTPCClusterFinder& clusterer, GPUSharedMemory& s, int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, int32_t firstHBF, int32_t tpcTimeBinCut);
+  static GPUd() void decode(GPUTPCClusterFinder& clusterer, GPUsharedref() GPUSharedMemory& s, int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, int32_t firstHBF, int32_t tpcTimeBinCut);
 
   typedef GPUTPCClusterFinder processorType;
   GPUhdi() static processorType* Processor(GPUConstantMem& processors)
@@ -59,7 +59,7 @@ class GPUTPCCFDecodeZS : public GPUKernelTemplate
   }
 
   template <int32_t iKernel = defaultKernel, typename... Args>
-  GPUd() static void Thread(int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, GPUSharedMemory& smem, processorType& clusterer, Args... args);
+  GPUd() static void Thread(int32_t nBlocks, int32_t nThreads, int32_t iBlock, int32_t iThread, GPUsharedref() GPUSharedMemory& smem, processorType& clusterer, Args... args);
 };
 
 class GPUTPCCFDecodeZSLinkBase : public GPUKernelTemplate