diff --git a/mlir/include/mlir/IR/OpBase.td b/mlir/include/mlir/IR/OpBase.td
index 8f6770f297ed..24e48b329d58 100644
--- a/mlir/include/mlir/IR/OpBase.td
+++ b/mlir/include/mlir/IR/OpBase.td
@@ -1586,6 +1586,7 @@ class Op<Dialect dialect, string mnemonic, list<OpTrait> props = []> {
   bit hasFolder = 0;
 
   // Op traits.
+  // Note: The list of traits will be uniqued by ODS.
   list<OpTrait> traits = props;
 
   // Additional code that will be added to the public part of the generated
diff --git a/mlir/lib/TableGen/Operator.cpp b/mlir/lib/TableGen/Operator.cpp
index 4529208a39c6..3825363bec00 100644
--- a/mlir/lib/TableGen/Operator.cpp
+++ b/mlir/lib/TableGen/Operator.cpp
@@ -23,6 +23,7 @@
 #include "mlir/TableGen/OpTrait.h"
 #include "mlir/TableGen/Predicate.h"
 #include "mlir/TableGen/Type.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
@@ -293,12 +294,18 @@ void tblgen::Operator::populateOpStructure() {
     results.push_back({name, TypeConstraint(resultDef)});
   }
 
-  auto traitListInit = def.getValueAsListInit("traits");
-  if (!traitListInit)
-    return;
-  traits.reserve(traitListInit->size());
-  for (auto traitInit : *traitListInit)
-    traits.push_back(OpTrait::create(traitInit));
+  // Create list of traits, skipping over duplicates: appending to lists in
+  // tablegen is easy, making them unique less so, so dedupe here.
+  if (auto traitList = def.getValueAsListInit("traits")) {
+    // This is uniquing based on pointers of the trait.
+    SmallPtrSet<const llvm::Init *, 32> traitSet;
+    traits.reserve(traitSet.size());
+    for (auto traitInit : *traitList) {
+      // Keep traits in the same order while skipping over duplicates.
+      if (traitSet.insert(traitInit).second)
+        traits.push_back(OpTrait::create(traitInit));
+    }
+  }
 
   // Handle regions
   auto *regionsDag = def.getValueAsDag("regions");
diff --git a/mlir/test/mlir-tblgen/op-decl.td b/mlir/test/mlir-tblgen/op-decl.td
index c0420cb19c1c..a217a139848b 100644
--- a/mlir/test/mlir-tblgen/op-decl.td
+++ b/mlir/test/mlir-tblgen/op-decl.td
@@ -9,7 +9,9 @@ def Test_Dialect : Dialect {
 class NS_Op<string mnemonic, list<OpTrait> traits> :
     Op<Test_Dialect, mnemonic, traits>;
 
-def NS_AOp : NS_Op<"a_op", [NoSideEffect]> {
+// NoSideEffect trait is included twice to ensure it gets uniqued during
+// emission.
+def NS_AOp : NS_Op<"a_op", [NoSideEffect, NoSideEffect]> {
   let arguments = (ins
     I32:$a,
     Variadic<F32>:$b,