diff --git a/objectivec/GPBExtensionField.h b/objectivec/GPBExtensionField.h
new file mode 100644
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+++ b/objectivec/GPBExtensionField.h
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#import <Foundation/Foundation.h>
+
+#import "GPBWireFormat.h"
+#import "GPBTypes.h"
+
+@class GPBCodedInputStream;
+@class GPBCodedOutputStream;
+@class GPBExtensionRegistry;
+@class GPBDescriptor;
+@class GPBExtensionDescriptor;
+
+@interface GPBExtensionField : NSObject<NSCopying>
+
+@property(nonatomic, readonly) int32_t fieldNumber;
+@property(nonatomic, readonly) GPBWireFormat wireType;
+@property(nonatomic, readonly) BOOL isRepeated;
+@property(nonatomic, readonly) GPBDescriptor *containingType;
+@property(nonatomic, readonly) id defaultValue;
+@property(nonatomic, readonly) GPBExtensionDescriptor *descriptor;
+
+@end