diff --git a/src/mathed/MathExtern.cpp b/src/mathed/MathExtern.cpp
index 52fa0cf0fa..e911f0babf 100644
--- a/src/mathed/MathExtern.cpp
+++ b/src/mathed/MathExtern.cpp
@@ -1421,11 +1421,46 @@ void write(MathData const & dat, WriteStream & wi)
 
 void writeString(docstring const & s, WriteStream & os)
 {
-	if (!os.latex() || os.lockedMode()) {
+	if (!os.latex()) {
 		os << (os.asciiOnly() ? escape(s) : s);
 		return;
 	}
 
+	if (os.lockedMode()) {
+		bool space;
+		docstring cmd;
+		for (char_type c : s) {
+			try {
+				Encodings::latexMathChar(c, true, os.encoding(), cmd, space);
+				os << cmd;
+				os.pendingSpace(space);
+			} catch (EncodingException const & e) {
+				switch (os.output()) {
+				case WriteStream::wsDryrun: {
+					os << "<" << _("LyX Warning: ")
+					   << _("uncodable character") << " '";
+					os << docstring(1, e.failed_char);
+					os << "'>";
+					break;
+				}
+				case WriteStream::wsPreview: {
+					// indicate the encoding error by a boxed '?'
+					os << "{\\fboxsep=1pt\\fbox{?}}";
+					LYXERR0("Uncodable character" << " '"
+						<< docstring(1, e.failed_char)
+						<< "'");
+					break;
+				}
+				case WriteStream::wsDefault:
+				default:
+					// throw again
+					throw(e);
+				}
+			}
+		}
+		return;
+	}
+
 	docstring::const_iterator cit = s.begin();
 	docstring::const_iterator end = s.end();
 
diff --git a/src/mathed/MathParser.cpp b/src/mathed/MathParser.cpp
index 539b1a3f02..868b920ebe 100644
--- a/src/mathed/MathParser.cpp
+++ b/src/mathed/MathParser.cpp
@@ -2077,7 +2077,7 @@ bool Parser::parse1(InsetMathGrid & grid, unsigned flags,
 							Encodings::MATH_CMD | Encodings::TEXT_CMD,
 							is_combining, termination);
 					}
-					if (c) {
+					if (c && buf->params().encoding().encodable(c)) {
 						if (termination) {
 							if (nextToken().cat() == catBegin) {
 								getToken();
diff --git a/status.23x b/status.23x
index 964a5397a5..dbd63f04da 100644
--- a/status.23x
+++ b/status.23x
@@ -54,6 +54,10 @@ Avoid using text mode for unicode symbols representable in math mode (bug 9616).
 
 - Avoid superfluous braces in the optional argument of a macro (bug 11552).
 
+- Do not replace a latex command with the corresponding symbol in the
+  unicodesymbols file, unless it can be encoded in the document encoding
+  (bug 11586).
+
 
 * USER INTERFACE