diff --git a/src/bufferparams.h b/src/bufferparams.h
index 80d7e606da..8f70225bfd 100644
--- a/src/bufferparams.h
+++ b/src/bufferparams.h
@@ -223,7 +223,7 @@ public:
 	AuthorList const & authors() const;
 
 	/// map of the file's author IDs to buffer author IDs
-	std::vector<int> author_map;
+	std::vector<unsigned int> author_map;
 	///
 	std::string const dvips_options() const;
 	///
diff --git a/src/text.C b/src/text.C
index 729c9cad09..47d782f0e0 100644
--- a/src/text.C
+++ b/src/text.C
@@ -328,14 +328,28 @@ void readParToken(Buffer const & buf, Paragraph & par, LyXLex & lex,
 		int aid;
 		lyx::time_type ct;
 		is >> aid >> ct;
-		change = Change(Change::INSERTED, bp.author_map[aid], ct);
+		if (aid >= bp.author_map.size()) {
+			buf.error(ErrorItem(_("Change tracking error"),
+					    bformat(_("Unknown author index for insertion: %1$d\n"), aid),
+					    par.id(), 0, par.size()));
+			
+			change = Change(Change::UNCHANGED);
+		} else
+			change = Change(Change::INSERTED, bp.author_map[aid], ct);
 	} else if (token == "\\change_deleted") {
 		lex.eatLine();
 		std::istringstream is(lex.getString());
 		int aid;
 		lyx::time_type ct;
 		is >> aid >> ct;
-		change = Change(Change::DELETED, bp.author_map[aid], ct);
+		if (aid >= bp.author_map.size()) {
+			buf.error(ErrorItem(_("Change tracking error"),
+					    bformat(_("Unknown author index for deletion: %1$d\n"), aid),
+					    par.id(), 0, par.size()));
+			
+			change = Change(Change::UNCHANGED);
+		} else
+			change = Change(Change::DELETED, bp.author_map[aid], ct);
 	} else {
 		lex.eatLine();
 		buf.error(ErrorItem(_("Unknown token"),