diff --git a/src/insets/InsetBibtex.cpp b/src/insets/InsetBibtex.cpp
index bee485eeb6..f606444ede 100644
--- a/src/insets/InsetBibtex.cpp
+++ b/src/insets/InsetBibtex.cpp
@@ -1276,7 +1276,7 @@ void InsetBibtex::docbook(XMLStream & xs, OutputParams const &) const
 				xs << xml::StartTag("keywordset") << xml::CR();
 				for (auto & kw: keywords) {
 					kw.erase(kw.begin(), std::find_if(kw.begin(), kw.end(),
-					                                  [](int c) {return !std::isspace(c);}));
+					                                  [](char_type c) {return !lyx::isSpace(c);}));
 					xs << xml::StartTag("keyword");
 					xs << kw;
 					xs << xml::EndTag("keyword");
diff --git a/src/xml.cpp b/src/xml.cpp
index dda39a4f3f..f96a19cdb5 100644
--- a/src/xml.cpp
+++ b/src/xml.cpp
@@ -143,7 +143,7 @@ docstring CompTag::writeTag() const
 		// automatically.
 		docstring attributes = escapeString(attr_, XMLStream::ESCAPE_NONE);
 		attributes.erase(attributes.begin(), std::find_if(attributes.begin(), attributes.end(),
-                                                          [](int c) {return !std::isspace(c);}));
+                                                          [](char_type c) {return !isSpace(c);}));
 		if (!attributes.empty()) {
 			output += ' ' + attributes;
 		}