diff --git a/onnxruntime/core/providers/coreml/builders/impl/flatten_op_builder.cc b/onnxruntime/core/providers/coreml/builders/impl/flatten_op_builder.cc
index d15db37fdd..4b6da84ff5 100644
--- a/onnxruntime/core/providers/coreml/builders/impl/flatten_op_builder.cc
+++ b/onnxruntime/core/providers/coreml/builders/impl/flatten_op_builder.cc
@@ -41,7 +41,7 @@ Status FlattenOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
   auto* coreml_flatten = layer->mutable_flattento2d();
 
   NodeAttrHelper helper(node);
-  const int64_t axis = helper.Get("axis ", 1);
+  const int64_t axis = helper.Get("axis", 1);
   coreml_flatten->set_axis(axis);
 
   *layer->mutable_input()->Add() = node.InputDefs()[0]->Name();
diff --git a/onnxruntime/test/providers/cpu/nn/flatten_op_test.cc b/onnxruntime/test/providers/cpu/nn/flatten_op_test.cc
index 7846b27713..a8dd7f24e7 100644
--- a/onnxruntime/test/providers/cpu/nn/flatten_op_test.cc
+++ b/onnxruntime/test/providers/cpu/nn/flatten_op_test.cc
@@ -2,6 +2,8 @@
 // Licensed under the MIT License.
 
 #include "gtest/gtest.h"
+
+#include "core/session/environment.h"
 #include "test/providers/provider_test_utils.h"
 
 namespace onnxruntime {
@@ -64,5 +66,37 @@ TEST_F(FlattenOpTest, Flatten_neg_axis3) {
   test_.Run(OpTester::ExpectResult::kExpectSuccess, "", {kTensorrtExecutionProvider});
 }
 
+// Regression test primarily for CoreML.
+// The CoreML EP implementation was not reading the axis attribute correctly causing an incorrect output shape to be
+// produced for a Flatten node. That issue gets hidden as the Tensor to write the output to is created by the
+// CoreML EP using the inferred output shape (which is correct) and we provide the Tensor's buffer but not the shape
+// when executing the CoreML model. As the flatten isn't changing or moving any data nothing breaks when we test
+// with only a Flatten node in the model.
+//
+// This test uses a model with a Flatten followed by a Mul which requires broadcasting. Both nodes are handled by
+// CoreML, so if the axis is not correctly processed the output from Flatten will not be broadcastable and the CoreML
+// model execution will fail.
+TEST(FlattenOpModelTest, Flatten_broadcast) {
+  auto model_uri = ORT_TSTR("testdata/flatten_broadcast.onnx");
+
+  std::shared_ptr<Model> model;
+  auto status = Model::Load(model_uri, model, nullptr, GetEnvironment().GetLoggingManager()->DefaultLogger());
+
+  OpTester tester("flatten_broadcast");
+  tester.SetModelCache(model);
+
+  tester.AddInput<float>("X", {4}, {0.f, 1.f, 2.f, 3.f});
+  tester.AddInput<float>("Y", {3, 4},
+                         {0.f, 1.f, 2.f, 3.f,
+                          4.f, 5.f, 6.f, 7.f,
+                          8.f, 9.f, 10.f, 11.f});
+  tester.AddOutput<float>("Z", {3, 4},
+                          {0.f, 1.f, 4.f, 9.f,
+                           0.f, 5.f, 12.f, 21.f,
+                           0.f, 9.f, 20.f, 33.f});
+
+  // disable TRT as it does not support axis=0 as used by the model
+  tester.Run(OpTester::ExpectResult::kExpectSuccess, "", {kTensorrtExecutionProvider});
+}
 }  // namespace test
 }  // namespace onnxruntime
diff --git a/onnxruntime/test/testdata/flatten_broadcast.onnx b/onnxruntime/test/testdata/flatten_broadcast.onnx
new file mode 100644
index 0000000000..098c0821e6
Binary files /dev/null and b/onnxruntime/test/testdata/flatten_broadcast.onnx differ