diff --git a/src/sample.c b/src/sample.c
index 3126be1..ab37a96 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -2070,7 +2070,7 @@
                                     const char *file, int line, char **err)
 {
 	if (args[1].data.sint <= 0 || args[1].data.sint > sizeof(unsigned long long)) {
-		memprintf(err, "chunk_size out of [1..%ld] range (%lld)", sizeof(unsigned long long), args[1].data.sint);
+		memprintf(err, "chunk_size out of [1..%u] range (%lld)", (uint)sizeof(unsigned long long), args[1].data.sint);
 		return 0;
 	}