diff --git a/test/minigzip.c b/test/minigzip.c
index 26c44ff..850458c 100644
--- a/test/minigzip.c
+++ b/test/minigzip.c
@@ -500,7 +500,7 @@
     char *infile, *outfile;
     FILE  *out;
     gzFile in;
-    z_size_t len = strlen(file);
+    unsigned len = strlen(file);
 
     if (len + strlen(GZ_SUFFIX) >= sizeof(buf)) {
         fprintf(stderr, "%s: filename too long\n", prog);