diff --git a/include/nlohmann/detail/input/binary_reader.hpp b/include/nlohmann/detail/input/binary_reader.hpp
index 2c22718870..58fd47c080 100644
--- a/include/nlohmann/detail/input/binary_reader.hpp
+++ b/include/nlohmann/detail/input/binary_reader.hpp
@@ -2798,11 +2798,11 @@ class binary_reader
     static void byte_swap(NumberType& number)
     {
         constexpr std::size_t sz = sizeof(number);
-        if (sz == 1)
+#ifdef __cpp_lib_byteswap
+        if constexpr (sz == 1)
         {
             return;
         }
-#ifdef __cpp_lib_byteswap
         // convert float types to int types of the same size
         using swap_t = std::conditional<sz == 2, std::uint16_t, typename std::conditional<sz == 4, std::uint32_t, std::uint64_t>::type>::type;
         swap_t& number_ref = reinterpret_cast<swap_t&>(number);
diff --git a/include/nlohmann/detail/input/input_adapters.hpp b/include/nlohmann/detail/input/input_adapters.hpp
index 97566dce32..fdbdc3f7be 100644
--- a/include/nlohmann/detail/input/input_adapters.hpp
+++ b/include/nlohmann/detail/input/input_adapters.hpp
@@ -141,7 +141,7 @@ class input_stream_adapter
         {
             is->clear(is->rdstate() | std::ios::eofbit);
         }
-        return res;
+        return static_cast<std::size_t>(res);
     }
 
   private:
@@ -179,7 +179,6 @@ class iterator_input_adapter
     template<class T>
     std::size_t get_elements(T* dest, std::size_t count = 1)
     {
-        size_t successful_read_chars = 0;
         auto ptr = reinterpret_cast<char*>(dest);
         for (std::size_t read_index = 0; read_index < count * sizeof(T); ++read_index)
         {
@@ -363,6 +362,7 @@ class wide_string_input_adapter
     std::size_t get_elements(T* dest, std::size_t count = 1)
     {
         JSON_THROW(other_error::create(500, "Unexpected get_elements call to wchar input adapter", nullptr));
+        return 0;
     }
 
   private:
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 94a27aceed..dfa1d30056 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -6286,7 +6286,7 @@ class input_stream_adapter
         {
             is->clear(is->rdstate() | std::ios::eofbit);
         }
-        return res;
+        return static_cast<std::size_t>(res);
     }
 
   private:
@@ -6324,7 +6324,6 @@ class iterator_input_adapter
     template<class T>
     std::size_t get_elements(T* dest, std::size_t count = 1)
     {
-        size_t successful_read_chars = 0;
         auto ptr = reinterpret_cast<char*>(dest);
         for (std::size_t read_index = 0; read_index < count * sizeof(T); ++read_index)
         {
@@ -6508,6 +6507,7 @@ class wide_string_input_adapter
     std::size_t get_elements(T* dest, std::size_t count = 1)
     {
         JSON_THROW(other_error::create(500, "Unexpected get_elements call to wchar input adapter", nullptr));
+        return 0;
     }
 
   private:
@@ -11989,11 +11989,11 @@ class binary_reader
     static void byte_swap(NumberType& number)
     {
         constexpr std::size_t sz = sizeof(number);
-        if (sz == 1)
+#ifdef __cpp_lib_byteswap
+        if constexpr (sz == 1)
         {
             return;
         }
-#ifdef __cpp_lib_byteswap
         // convert float types to int types of the same size
         using swap_t = std::conditional<sz == 2, std::uint16_t, typename std::conditional<sz == 4, std::uint32_t, std::uint64_t>::type>::type;
         swap_t& number_ref = reinterpret_cast<swap_t&>(number);