diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -493,6 +493,13 @@
     setLibcallName(RTLIB::MULO_I128, nullptr);
   }
 
+  if (Subtarget.isGP64bit())
+    setMaxAtomicSizeInBitsSupported(64);
+  else if (Subtarget.hasMips2())
+    setMaxAtomicSizeInBitsSupported(32);
+  else
+    setMaxAtomicSizeInBitsSupported(0);
+
   setMinFunctionAlignment(Subtarget.isGP64bit() ? Align(8) : Align(4));
 
   // The arguments on the stack are defined in terms of 4-byte slots on O32