return 0 on misses, not -1.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 714bddd..c5e87a8 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -172,7 +172,7 @@
         if (set[i] == chr)
             return 1;
 
-    return -1;
+    return 0;
 }
 
 #define BLOOM_MEMBER(mask, chr, set, setlen)\