diff --git a/include/json/value.h b/include/json/value.h
index 62a323b..ae6f661 100644
--- a/include/json/value.h
+++ b/include/json/value.h
@@ -172,7 +172,7 @@ private:
     CZString(const char* cstr, DuplicationPolicy allocate);
     CZString(const CZString& other);
     ~CZString();
-    CZString& operator=(CZString other);
+    CZString &operator=(const CZString &other);
     bool operator<(const CZString& other) const;
     bool operator==(const CZString& other) const;
     ArrayIndex index() const;
@@ -241,7 +241,7 @@ Json::Value obj_value(Json::objectValue); // {}
   ~Value();
 
   // Deep copy, then swap(other).
-  Value& operator=(Value other);
+  Value &operator=(const Value &other);
   /// Swap everything.
   void swap(Value& other);
   /// Swap values but leave comments and source offsets in place.
diff --git a/src/lib_json/json_value.cpp b/src/lib_json/json_value.cpp
index f9139c7..16bfad9 100644
--- a/src/lib_json/json_value.cpp
+++ b/src/lib_json/json_value.cpp
@@ -192,8 +192,9 @@ void Value::CZString::swap(CZString& other) {
   std::swap(index_, other.index_);
 }
 
-Value::CZString& Value::CZString::operator=(CZString other) {
-  swap(other);
+Value::CZString &Value::CZString::operator=(const CZString &other) {
+  CZString temp(other);
+  swap(temp);
   return *this;
 }
 
@@ -409,8 +410,9 @@ Value::~Value() {
     delete[] comments_;
 }
 
-Value& Value::operator=(Value other) {
-  swap(other);
+Value &Value::operator=(const Value &other) {
+  Value temp(other);
+  swap(temp);
   return *this;
 }