diff --git a/include/nlohmann/detail/input/input_adapters.hpp b/include/nlohmann/detail/input/input_adapters.hpp
index 40560ca1..f8155faa 100644
--- a/include/nlohmann/detail/input/input_adapters.hpp
+++ b/include/nlohmann/detail/input/input_adapters.hpp
@@ -126,7 +126,7 @@ class wide_string_input_adapter : public input_adapter_protocol
         // check if buffer needs to be filled
         if (utf8_bytes_index == utf8_bytes_filled)
         {
-            fill_buffer(sizeof(typename WideStringType::value_type));
+            fill_buffer<sizeof(typename WideStringType::value_type)>();
 
             assert(utf8_bytes_filled > 0);
             assert(utf8_bytes_index == 0);
@@ -139,16 +139,16 @@ class wide_string_input_adapter : public input_adapter_protocol
     }
 
   private:
-    void fill_buffer(size_t size)
+    template<size_t T>
+    void fill_buffer()
     {
-        if (2 == size)
-        {
-            fill_buffer_utf16();
-        }
-        else
-        {
-            fill_buffer_utf32();
-        }
+        fill_buffer_utf32();
+    }
+
+    template<>
+    void fill_buffer<2>()
+    {
+        fill_buffer_utf16();
     }
     
     void fill_buffer_utf16()
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 7af55b3a..c19ee6c9 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -2004,7 +2004,7 @@ class wide_string_input_adapter : public input_adapter_protocol
         // check if buffer needs to be filled
         if (utf8_bytes_index == utf8_bytes_filled)
         {
-            fill_buffer(sizeof(typename WideStringType::value_type));
+            fill_buffer<sizeof(typename WideStringType::value_type)>();
 
             assert(utf8_bytes_filled > 0);
             assert(utf8_bytes_index == 0);
@@ -2017,18 +2017,18 @@ class wide_string_input_adapter : public input_adapter_protocol
     }
 
   private:
-    void fill_buffer(size_t size)
+    template<size_t T>
+    void fill_buffer()
     {
-        if (2 == size)
-        {
-            fill_buffer_utf16();
-        }
-        else
-        {
-            fill_buffer_utf32();
-        }
+        fill_buffer_utf32();
     }
 
+    template<>
+    void fill_buffer<2>()
+    {
+        fill_buffer_utf16();
+    }
+    
     void fill_buffer_utf16()
     {
         utf8_bytes_index = 0;