loader: fix mismatch size warning
diff --git a/loader/murmurhash.h b/loader/murmurhash.h
index 3fa072c..62e4d09 100644
--- a/loader/murmurhash.h
+++ b/loader/murmurhash.h
@@ -22,7 +22,7 @@
  */
 
 uint32_t
-murmurhash (const char *key, uint32_t len, uint32_t seed);
+murmurhash (const char *key, size_t len, uint32_t seed);
 
 #ifdef __cplusplus
 }