diff --git a/include/villas/io.h b/include/villas/io.h
index 83e0a0c03..969daca15 100644
--- a/include/villas/io.h
+++ b/include/villas/io.h
@@ -76,9 +76,9 @@ int io_open(struct io *io, const char *uri);
 
 int io_close(struct io *io);
 
-int io_print(struct io *io, struct sample *smps[], size_t cnt);
+int io_print(struct io *io, struct sample *smps[], unsigned cnt);
 
-int io_scan(struct io *io, struct sample *smps[], size_t cnt);
+int io_scan(struct io *io, struct sample *smps[], unsigned cnt);
 
 int io_eof(struct io *io);
 
diff --git a/lib/io.c b/lib/io.c
index 564c51fe7..0bd7d85ea 100644
--- a/lib/io.c
+++ b/lib/io.c
@@ -212,7 +212,7 @@ void io_rewind(struct io *io)
 		: io_stream_rewind(io);
 }
 
-int io_print(struct io *io, struct sample *smps[], size_t cnt)
+int io_print(struct io *io, struct sample *smps[], unsigned cnt)
 {
 	int ret;
 
@@ -247,7 +247,7 @@ int io_print(struct io *io, struct sample *smps[], size_t cnt)
 	return ret;
 }
 
-int io_scan(struct io *io, struct sample *smps[], size_t cnt)
+int io_scan(struct io *io, struct sample *smps[], unsigned cnt)
 {
 	int ret;