diff --git a/src/borg/chunker.pyx b/src/borg/chunker.pyx
index bbe47ceca..d2b44f686 100644
--- a/src/borg/chunker.pyx
+++ b/src/borg/chunker.pyx
@@ -50,11 +50,11 @@ cdef class Chunker:
         return chunker_process(self.chunker)
 
 
-def buzhash(unsigned char *data, unsigned long seed):
+def buzhash(data, unsigned long seed):
     cdef uint32_t *table
     cdef uint32_t sum
     table = buzhash_init_table(seed & 0xffffffff)
-    sum = c_buzhash(data, len(data), table)
+    sum = c_buzhash(<const unsigned char *> data, len(data), table)
     free(table)
     return sum