diff --git a/c_api/index_io_c_ex.cpp b/c_api/index_io_c_ex.cpp
index 2d29e892b5..ef2110dbe6 100644
--- a/c_api/index_io_c_ex.cpp
+++ b/c_api/index_io_c_ex.cpp
@@ -30,7 +30,7 @@ int faiss_write_index_buf(const FaissIndex* idx, size_t* size, unsigned char** b
     CATCH_AND_HANDLE
 }
 
-int faiss_read_index_buf(const uint8_t* buf, int size, int io_flags, FaissIndex** p_out) {
+int faiss_read_index_buf(const uint8_t* buf, size_t size, int io_flags, FaissIndex** p_out) {
     try {
         faiss::BufIOReader reader;
         reader.buf = buf;
diff --git a/c_api/index_io_c_ex.h b/c_api/index_io_c_ex.h
index 64435ce180..77a3f999b1 100644
--- a/c_api/index_io_c_ex.h
+++ b/c_api/index_io_c_ex.h
@@ -27,7 +27,7 @@ int faiss_write_index_buf(const FaissIndex* idx, size_t* buf_size, unsigned char
 
 /** Read index from buffer
  */
-int faiss_read_index_buf(const unsigned char* buf, int limit, int io_flags,
+int faiss_read_index_buf(const unsigned char* buf, size_t limit, int io_flags,
         FaissIndex** p_out);
 
 #ifdef __cplusplus