diff --git a/desc/protoparse/linker_test.go b/desc/protoparse/linker_test.go
index 1f05f7e8..3365e543 100644
--- a/desc/protoparse/linker_test.go
+++ b/desc/protoparse/linker_test.go
@@ -868,6 +868,16 @@ func TestLinkerValidation(t *testing.T) {
 			},
 			"foo.proto:9:6: message foo.bar.Baz: option (foo.bar.any): could not resolve type reference type.googleapis.com/Foo",
 		},
+		{
+			map[string]string{
+				"foo.proto": "syntax = \"proto3\";\n" +
+					"import \"google/protobuf/descriptor.proto\";\n" +
+					"extend google.protobuf.MessageOptions {\n" +
+					"  string foobar = 10001 [json_name=\"FooBar\"];\n" +
+					"}\n",
+			},
+			"foo.proto:4:26: field foobar: option json_name is not allowed on extensions",
+		},
 	}
 	for i, tc := range testCases {
 		acc := func(filename string) (io.ReadCloser, error) {
diff --git a/desc/protoparse/options.go b/desc/protoparse/options.go
index c13cf15d..f9f306bb 100644
--- a/desc/protoparse/options.go
+++ b/desc/protoparse/options.go
@@ -696,7 +696,7 @@ func interpretFileOptions(l *linker, r *parseResult, fd fileDescriptorish) error
 		}
 	}
 	for _, fld := range fd.GetExtensions() {
-		if err := interpretFieldOptions(l, r, fld); err != nil {
+		if err := interpretFieldOptions(l, r, fld, true); err != nil {
 			return err
 		}
 	}
@@ -740,7 +740,7 @@ func interpretMessageOptions(l *linker, r *parseResult, md msgDescriptorish) err
 		}
 	}
 	for _, fld := range md.GetFields() {
-		if err := interpretFieldOptions(l, r, fld); err != nil {
+		if err := interpretFieldOptions(l, r, fld, false); err != nil {
 			return err
 		}
 	}
@@ -755,7 +755,7 @@ func interpretMessageOptions(l *linker, r *parseResult, md msgDescriptorish) err
 		}
 	}
 	for _, fld := range md.GetNestedExtensions() {
-		if err := interpretFieldOptions(l, r, fld); err != nil {
+		if err := interpretFieldOptions(l, r, fld, true); err != nil {
 			return err
 		}
 	}
@@ -782,7 +782,7 @@ func interpretMessageOptions(l *linker, r *parseResult, md msgDescriptorish) err
 	return nil
 }
 
-func interpretFieldOptions(l *linker, r *parseResult, fld fldDescriptorish) error {
+func interpretFieldOptions(l *linker, r *parseResult, fld fldDescriptorish, isExtension bool) error {
 	opts := fld.GetFieldOptions()
 	if len(opts.GetUninterpretedOption()) > 0 {
 		uo := opts.UninterpretedOption
@@ -804,6 +804,10 @@ func interpretFieldOptions(l *linker, r *parseResult, fld fldDescriptorish) erro
 				if err := r.errs.handleErrorWithPos(optNode.GetValue().Start(), "%s: expecting string value for json_name option", scope); err != nil {
 					return err
 				}
+			} else if isExtension {
+				if err := r.errs.handleErrorWithPos(optNode.GetName().Start(), "%s: option json_name is not allowed on extensions", scope); err != nil {
+					return err
+				}
 			} else {
 				fld.AsFieldDescriptorProto().JsonName = proto.String(string(opt.StringValue))
 			}