diff --git a/src/insets/InsetLayout.cpp b/src/insets/InsetLayout.cpp
index 2b71a2256a..7b0f8d0843 100644
--- a/src/insets/InsetLayout.cpp
+++ b/src/insets/InsetLayout.cpp
@@ -183,6 +183,12 @@ bool InsetLayout::read(Lexer & lex, TextClass const & tclass)
 		// way this sort of thing is handled in Layout::read(), namely, by
 		// using the Lexer.
 		case IL_LYXTYPE: {
+			// make sure that we have the right sort of name.
+			if (name_.substr(0,5) != from_ascii("Flex:")) {
+				LYXERR0("Flex insets must have names of the form `Flex:<name>'.\n"
+				        "This one has the name `" << to_utf8(name_) << "'\n"
+				        "Ignoring LyXType declaration.");
+			}
 			string lt;
 			lex >> lt;
 			lyxtype_ = translateLyXType(lt);