diff --git a/libfec/include/fec/io.h b/libfec/include/fec/io.h
index 7f8122c..5e597ac 100644
--- a/libfec/include/fec/io.h
+++ b/libfec/include/fec/io.h
@@ -123,7 +123,7 @@
     public:
         io() : handle_(nullptr, fec_close) {}
 
-        io(const std::string& fn, int mode = O_RDONLY, int flags = 0,
+        explicit io(const std::string& fn, int mode = O_RDONLY, int flags = 0,
                 int roots = FEC_DEFAULT_ROOTS) : handle_(nullptr, fec_close) {
             open(fn, mode, flags, roots);
         }