diff --git a/mlir/lib/Conversion/OpenACCToLLVM/OpenACCToLLVM.cpp b/mlir/lib/Conversion/OpenACCToLLVM/OpenACCToLLVM.cpp
--- a/mlir/lib/Conversion/OpenACCToLLVM/OpenACCToLLVM.cpp
+++ b/mlir/lib/Conversion/OpenACCToLLVM/OpenACCToLLVM.cpp
@@ -70,6 +70,8 @@
 // Conversion patterns
 //===----------------------------------------------------------------------===//
 
+namespace {
+
 template <typename Op>
 class LegalizeDataOpForLLVMTranslation : public ConvertOpToLLVMPattern<Op> {
   using ConvertOpToLLVMPattern<Op>::ConvertOpToLLVMPattern;
@@ -131,6 +133,7 @@
     return success();
   }
 };
+} // namespace
 
 void mlir::populateOpenACCToLLVMConversionPatterns(
     LLVMTypeConverter &converter, OwningRewritePatternList &patterns) {