diff --git a/src/calibre/srv/fast_css_transform.cpp b/src/calibre/srv/fast_css_transform.cpp
index 8315ee3b17..ccdf80dd81 100644
--- a/src/calibre/srv/fast_css_transform.cpp
+++ b/src/calibre/srv/fast_css_transform.cpp
@@ -297,11 +297,13 @@ class Token {
 
         void serialize_string(std::u32string &out) const {
             const char32_t delim = text.find('"') == std::u32string::npos ? '"' : '\'';
+            out.push_back(delim);
             for (const auto ch : text) {
                 if (ch == '\n') out.append({'\\', '\n'});
                 else if (ch == delim || ch == '\\') serialize_escaped_char(ch, out);
                 else out.push_back(ch);
             }
+            out.push_back(delim);
         }
 
     public:
@@ -313,7 +315,7 @@ class Token {
         Token(const TokenType type, const char32_t ch, size_t out_pos) :
 			type(type), text(), unit_at(0), out_pos(out_pos) {
 				text.reserve(16);
-				text.push_back(ch);
+				if (ch) text.push_back(ch);
 			}
 
         Token(const Token& other) :
diff --git a/src/calibre/srv/tests/fast_css_transform.py b/src/calibre/srv/tests/fast_css_transform.py
index 58b3de9620..c1d8d14387 100644
--- a/src/calibre/srv/tests/fast_css_transform.py
+++ b/src/calibre/srv/tests/fast_css_transform.py
@@ -23,7 +23,15 @@ class TestTransform(SimpleTest):
             self.ae(transform_properties(src, is_declaration=is_declaration, url_callback=url_callback), expected)
 
         d(r'f\ont-s\69z\65 : 16\px', 'font-size: 1rem')
+        d('font -size: 16px', 'font -size: 16px')
         d('font-size: 16px', 'font-size: 1rem')
         d('fOnt-size :16px', 'fOnt-size :1rem')
         d('font-size:2%', 'font-size:2%')
-        d('font-size: 72pt; color: red; font-size: 2in', 'font-size: 6rem; color: red; font-size: 12rem')
+        d('font-size: 72pt; margin: 20px; font-size: 2in', 'font-size: 6rem; margin: 20px; font-size: 12rem')
+        d(r'''font: "some 'name" 32px''', 'font: "some \'name" 2rem')
+        d(r'''font: 'some "name' 32px''', 'font: \'some "name\' 2rem')
+        d(r'''font: 'some \n ame' 32px''', 'font: "some n ame" 2rem')
+        d('''font: 'some \\\nname' 32px''', 'font: "some name" 2rem')
+        d('font: sans-serif 16px/3', 'font: sans-serif 1rem/3')
+
+        d('-epub-writing-mode: a; -webkit-writing-mode: b; writing-mode: c', 'writing-mode: a; writing-mode: b; writing-mode: c')