diff --git a/src/lib_json/json_value.cpp b/src/lib_json/json_value.cpp
index 8fbce5425..cc7d4d3d8 100644
--- a/src/lib_json/json_value.cpp
+++ b/src/lib_json/json_value.cpp
@@ -125,7 +125,7 @@ inline static void decodePrefixedString(
     unsigned* length, char const** value)
 {
   if (!isPrefixed) {
-    *length = strlen(prefixed);
+    *length = static_cast<unsigned>(strlen(prefixed));
     *value = prefixed;
   } else {
     *length = *reinterpret_cast<unsigned const*>(prefixed);
diff --git a/src/lib_json/json_writer.cpp b/src/lib_json/json_writer.cpp
index 3be34d9e6..2f940c8a4 100644
--- a/src/lib_json/json_writer.cpp
+++ b/src/lib_json/json_writer.cpp
@@ -354,7 +354,7 @@ void FastWriter::writeValue(const Value& value) {
       const std::string& name = *it;
       if (it != members.begin())
         document_ += ',';
-      document_ += valueToQuotedStringN(name.data(), name.length());
+      document_ += valueToQuotedStringN(name.data(), static_cast<unsigned>(name.length()));
       document_ += yamlCompatiblityEnabled_ ? ": " : ":";
       writeValue(value[name]);
     }
@@ -914,7 +914,7 @@ void BuiltStyledStreamWriter::writeValue(Value const& value) {
         std::string const& name = *it;
         Value const& childValue = value[name];
         writeCommentBeforeValue(childValue);
-        writeWithIndent(valueToQuotedStringN(name.data(), name.length()));
+        writeWithIndent(valueToQuotedStringN(name.data(), static_cast<unsigned>(name.length())));
         *sout_ << colonSymbol_;
         writeValue(childValue);
         if (++it == members.end()) {