diff --git a/include/nlohmann/detail/output/serializer.hpp b/include/nlohmann/detail/output/serializer.hpp
index c2823487e..647f89673 100644
--- a/include/nlohmann/detail/output/serializer.hpp
+++ b/include/nlohmann/detail/output/serializer.hpp
@@ -832,7 +832,9 @@ class serializer
 
         // the actual conversion
         // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(), "%.*g", d, x);
+        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(),
+                                             std::is_same<number_float_t, long double>::value ? "%.*Lg" : "%.*g",
+                                             d, x);
 
         // negative value indicates an error
         JSON_ASSERT(len > 0);
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 07dea3c4a..3ccfee92a 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -19538,7 +19538,9 @@ class serializer
 
         // the actual conversion
         // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(), "%.*g", d, x);
+        std::ptrdiff_t len = (std::snprintf)(number_buffer.data(), number_buffer.size(),
+                                             std::is_same<number_float_t, long double>::value ? "%.*Lg" : "%.*g",
+                                             d, x);
 
         // negative value indicates an error
         JSON_ASSERT(len > 0);