diff --git a/Python/pyhash.c b/Python/pyhash.c
index 4c0b929..ba224ee 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -366,7 +366,7 @@
 static uint64_t
 siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     uint64_t b = (uint64_t)src_sz << 56;
-    const uint8_t *in = (uint8_t*)src;
+    const uint8_t *in = (const uint8_t*)src;
 
     uint64_t v0 = k0 ^ 0x736f6d6570736575ULL;
     uint64_t v1 = k1 ^ 0x646f72616e646f6dULL;