diff --git a/overviewer_core/src/overviewer.h b/overviewer_core/src/overviewer.h
index 860dfa3..7440274 100644
--- a/overviewer_core/src/overviewer.h
+++ b/overviewer_core/src/overviewer.h
@@ -136,7 +136,7 @@ extern unsigned int max_blockid;
 extern unsigned int max_data;
 extern unsigned char *block_properties;
 static inline int
-block_has_property(unsigned char b, BlockProperty prop) {
+block_has_property(unsigned short b, BlockProperty prop) {
     if (b >= max_blockid || !(block_properties[b] & (1 << KNOWN))) {
         /* block is unknown, return defaults */
         if (prop == TRANSPARENT)