diff --git a/src/papi/lz4/api.h b/src/papi/lz4/api.h
index fa3d21d..e5d348f 100644
--- a/src/papi/lz4/api.h
+++ b/src/papi/lz4/api.h
@@ -53,7 +53,7 @@ namespace lz4 { namespace api {
                 or 0, if input size is too large ( > MAX_INPUT_SIZE)
     */
     int compressBound(int inputSize);
-    int compressBound(const span<char> input);
+    int compressBound(const span<const char> input);
 
     /**
         Compresses buffer 'source' into already allocated 'dest' buffer.
@@ -75,12 +75,12 @@ namespace lz4 { namespace api {
     */
     int compress_default(const span<const char> source, const span<char> dest);
 
-    int decompress_safe (const span<char> source, span<char> dest);
+    int decompress_safe (const span<const char> source, span<char> dest);
     int sizeofState();
-    int compress_fast_extState(span<byte> state, const span<char> source, span<char> dest, int acceleration);
+    int compress_fast_extState(span<byte> state, const span<const char> source, span<char> dest, int acceleration);
     int compress_destSize (span<char>& source, span<char> dest);
-    int decompress_fast (const span<char> source, span<char> dest, int uncompressedSize);
-    int decompress_safe_partial (const span<char> source, span<char> dest, int targetOutputSize);
+    int decompress_fast (const span<const char> source, span<char> dest, int uncompressedSize);
+    int decompress_safe_partial (const span<const char> source, span<char> dest, int targetOutputSize);
 };
 };
 
diff --git a/src/papi/lz4/api_impl.h b/src/papi/lz4/api_impl.h
index 1ac4b6b..a0f4ba8 100644
--- a/src/papi/lz4/api_impl.h
+++ b/src/papi/lz4/api_impl.h
@@ -8,7 +8,7 @@ namespace lz4 { namespace api {
         return _detail::LZ4_compressBound(inputSize);
         };
 
-    inline int compressBound(const span<char> input)
+    inline int compressBound(const span<const char> input)
         {
         return _detail::LZ4_compressBound(input.length());
         };
@@ -18,7 +18,7 @@ namespace lz4 { namespace api {
         return _detail::LZ4_compress_default(source.data(), dest.data(), source.length(), dest.length());
         };
 
-    inline int decompress_safe (const span<char> source, span<char>  dest)
+    inline int decompress_safe (const span<const char> source, span<char>  dest)
         {
         return _detail::LZ4_decompress_safe(source.data(), dest.data(), source.length(), dest.length());
         };
@@ -28,7 +28,7 @@ namespace lz4 { namespace api {
         return _detail::LZ4_sizeofState();
         };
 
-    inline int compress_fast_extState(span<byte> state, const span<char> source, span<char> dest, int acceleration)
+    inline int compress_fast_extState(span<byte> state, const span<const char> source, span<char> dest, int acceleration)
         {
         return _detail::LZ4_compress_fast_extState(state.data(), source.data(), dest.data(), source.length(), dest.length(), acceleration);
         };
@@ -44,12 +44,12 @@ namespace lz4 { namespace api {
         return _detail::LZ4_compress_destSize(source.data(), dest.data(), const_cast<int*>(&sourceUsed), dest.length());
         };
 
-    inline int decompress_fast (const span<char> source, span<char> dest, int uncompressedSize)
+    inline int decompress_fast (const span<const char> source, span<char> dest, int uncompressedSize)
         {
         return _detail::LZ4_decompress_fast(source.data(), dest.data(), uncompressedSize);
         };
 
-    inline int decompress_safe_partial (const span<char> source, span<char> dest, int targetOutputSize)
+    inline int decompress_safe_partial (const span<const char> source, span<char> dest, int targetOutputSize)
         {
         return _detail::LZ4_decompress_safe_partial (source.data(), dest.data(), source.length(), targetOutputSize, dest.length());    
         };