diff --git a/desc/protoparse/linker.go b/desc/protoparse/linker.go
index 34350263..7bc27b08 100644
--- a/desc/protoparse/linker.go
+++ b/desc/protoparse/linker.go
@@ -71,7 +71,7 @@ func (l *linker) linkFiles() (map[string]*desc.FileDescriptor, error) {
 		}
 		// we should now have any message_set_wire_format options parsed
 		// and can do further validation on tag ranges
-		if err := checkExtensionsInFile(fd, r); err != nil {
+		if err := l.checkExtensionsInFile(fd, r); err != nil {
 			return nil, err
 		}
 	}
@@ -999,3 +999,59 @@ func (l *linker) checkForUnusedImports(filename string) {
 		}
 	}
 }
+
+func (l *linker) checkExtensionsInFile(fd *desc.FileDescriptor, res *parseResult) error {
+	for _, fld := range fd.GetExtensions() {
+		if err := l.checkExtension(fld, res); err != nil {
+			return err
+		}
+	}
+	for _, md := range fd.GetMessageTypes() {
+		if err := l.checkExtensionsInMessage(md, res); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (l *linker) checkExtensionsInMessage(md *desc.MessageDescriptor, res *parseResult) error {
+	for _, fld := range md.GetNestedExtensions() {
+		if err := l.checkExtension(fld, res); err != nil {
+			return err
+		}
+	}
+	for _, nmd := range md.GetNestedMessageTypes() {
+		if err := l.checkExtensionsInMessage(nmd, res); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (l *linker) checkExtension(fld *desc.FieldDescriptor, res *parseResult) error {
+	// NB: It's a little gross that we don't enforce these in validateBasic().
+	// But requires some minimal linking to resolve the extendee, so we can
+	// interrogate its descriptor.
+	if fld.GetOwner().GetMessageOptions().GetMessageSetWireFormat() {
+		// Message set wire format requires that all extensions be messages
+		// themselves (no scalar extensions)
+		if fld.GetType() != dpb.FieldDescriptorProto_TYPE_MESSAGE {
+			pos := res.getFieldNode(fld.AsFieldDescriptorProto()).FieldType().Start()
+			return l.errs.handleErrorWithPos(pos, "messages with message-set wire format cannot contain scalar extensions, only messages")
+		}
+		if fld.IsRepeated() {
+			pos := res.getFieldNode(fld.AsFieldDescriptorProto()).FieldLabel().Start()
+			return l.errs.handleErrorWithPos(pos, "messages with message-set wire format cannot contain repeated extensions, only optional")
+		}
+	} else {
+		// In validateBasic() we just made sure these were within bounds for any message. But
+		// now that things are linked, we can check if the extendee is messageset wire format
+		// and, if not, enforce tighter limit.
+		if fld.GetNumber() > internal.MaxNormalTag {
+			pos := res.getFieldNode(fld.AsFieldDescriptorProto()).FieldTag().Start()
+			return l.errs.handleErrorWithPos(pos, "tag number %d is higher than max allowed tag number (%d)", fld.GetNumber(), internal.MaxNormalTag)
+		}
+	}
+
+	return nil
+}
diff --git a/desc/protoparse/linker_test.go b/desc/protoparse/linker_test.go
index 3365e543..8cbcee23 100644
--- a/desc/protoparse/linker_test.go
+++ b/desc/protoparse/linker_test.go
@@ -413,6 +413,12 @@ func TestLinkerValidation(t *testing.T) {
 			},
 			"", // should succeed
 		},
+		{
+			map[string]string{
+				"foo.proto": "message Foo { option message_set_wire_format = true; extensions 1 to 100; } extend Foo { repeated Foo bar = 1; }",
+			},
+			"foo.proto:1:90: messages with message-set wire format cannot contain repeated extensions, only optional",
+		},
 		{
 			map[string]string{
 				"foo.proto": "message Foo { extensions 1 to max; } extend Foo { optional int32 bar = 536870912; }",
diff --git a/desc/protoparse/parser.go b/desc/protoparse/parser.go
index d9801cd5..5300aab6 100644
--- a/desc/protoparse/parser.go
+++ b/desc/protoparse/parser.go
@@ -817,58 +817,6 @@ func checkTag(pos *SourcePos, v uint64, maxTag int32) error {
 	return nil
 }
 
-func checkExtensionsInFile(fd *desc.FileDescriptor, res *parseResult) error {
-	for _, fld := range fd.GetExtensions() {
-		if err := checkExtension(fld, res); err != nil {
-			return err
-		}
-	}
-	for _, md := range fd.GetMessageTypes() {
-		if err := checkExtensionsInMessage(md, res); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-func checkExtensionsInMessage(md *desc.MessageDescriptor, res *parseResult) error {
-	for _, fld := range md.GetNestedExtensions() {
-		if err := checkExtension(fld, res); err != nil {
-			return err
-		}
-	}
-	for _, nmd := range md.GetNestedMessageTypes() {
-		if err := checkExtensionsInMessage(nmd, res); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-func checkExtension(fld *desc.FieldDescriptor, res *parseResult) error {
-	// NB: It's a little gross that we don't enforce these in validateBasic().
-	// But requires some minimal linking to resolve the extendee, so we can
-	// interrogate its descriptor.
-	if fld.GetOwner().GetMessageOptions().GetMessageSetWireFormat() {
-		// Message set wire format requires that all extensions be messages
-		// themselves (no scalar extensions)
-		if fld.GetType() != dpb.FieldDescriptorProto_TYPE_MESSAGE {
-			pos := res.getFieldNode(fld.AsFieldDescriptorProto()).FieldType().Start()
-			return errorWithPos(pos, "messages with message-set wire format cannot contain scalar extensions, only messages")
-		}
-	} else {
-		// In validateBasic() we just made sure these were within bounds for any message. But
-		// now that things are linked, we can check if the extendee is messageset wire format
-		// and, if not, enforce tighter limit.
-		if fld.GetNumber() > internal.MaxNormalTag {
-			pos := res.getFieldNode(fld.AsFieldDescriptorProto()).FieldTag().Start()
-			return errorWithPos(pos, "tag number %d is higher than max allowed tag number (%d)", fld.GetNumber(), internal.MaxNormalTag)
-		}
-	}
-
-	return nil
-}
-
 func aggToString(agg []*ast.MessageFieldNode, buf *bytes.Buffer) {
 	buf.WriteString("{")
 	for _, a := range agg {