diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -357,6 +357,11 @@
   // condition branches.
   setJumpIsExpensive(true);
 
+  // Force atomics to be expanded if the ISA doesn't support them: PR4219
+  setMinCmpXchgSizeInBits(32);
+  setMaxAtomicSizeInBitsSupported(64);
+  setSupportsUnalignedAtomics(false);
+
   // Wide divides are _very_ slow. Try to reduce the width of the divide if
   // possible.
   addBypassSlowDiv(64, 32);