diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index 73d2007faa..ae06ff89f4 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -1675,7 +1675,7 @@ void Buffer::writeLaTeXSource(otexstream & os,
 
 	// XeTeX with TeX fonts is only safe with ASCII encoding,
 	// See #9740 and FIXME in BufferParams::encoding()
-	if (params().useNonTeXFonts && (runparams.flavor == OutputParams::XETEX))
+	if (!params().useNonTeXFonts && (runparams.flavor == OutputParams::XETEX))
 		runparams.encoding = encodings.fromLyXName("ascii");
 
 	// If we are compiling a file standalone, even if this is the