diff --git a/mlir/lib/Parser/Parser.cpp b/mlir/lib/Parser/Parser.cpp
--- a/mlir/lib/Parser/Parser.cpp
+++ b/mlir/lib/Parser/Parser.cpp
@@ -1706,6 +1706,13 @@
   if (parseCommaSeparatedListUntil(Token::r_brace, parseElt))
     return failure();
 
+  llvm::SmallDenseSet<Identifier> uniquifier;
+  for (auto &namedAttr : attributes) {
+    if (!uniquifier.insert(namedAttr.first).second) {
+      return emitError("duplicate key in dictionary attribute");
+    }
+  }
+
   return success();
 }
 
diff --git a/mlir/test/IR/invalid.mlir b/mlir/test/IR/invalid.mlir
--- a/mlir/test/IR/invalid.mlir
+++ b/mlir/test/IR/invalid.mlir
@@ -1489,3 +1489,10 @@
   } : () -> ()
   return
 }
+
+// -----
+
+func @duplicate_dictionary_attr_key() {
+  // expected-error @+1 {{duplicate key in dictionary attribute}}
+  "foo.op"() {a, a} : () -> ()
+}