diff --git a/src/crypto/siphash.h b/src/crypto/siphash.h
--- a/src/crypto/siphash.h
+++ b/src/crypto/siphash.h
@@ -14,7 +14,8 @@
 private:
     uint64_t v[4];
     uint64_t tmp;
-    int count;
+    // Only the low 8 bits of the input size matter.
+    uint8_t count;
 
 public:
     /** Construct a SipHash calculator initialized with 128-bit key (k0, k1) */
diff --git a/src/crypto/siphash.cpp b/src/crypto/siphash.cpp
--- a/src/crypto/siphash.cpp
+++ b/src/crypto/siphash.cpp
@@ -55,7 +55,7 @@
 CSipHasher &CSipHasher::Write(const uint8_t *data, size_t size) {
     uint64_t v0 = v[0], v1 = v[1], v2 = v[2], v3 = v[3];
     uint64_t t = tmp;
-    int c = count;
+    uint8_t c = count;
 
     while (size--) {
         t |= uint64_t(*(data++)) << (8 * (c % 8));