diff --git a/halfsiphash.c b/halfsiphash.c
index adfe1d2..689e125 100644
--- a/halfsiphash.c
+++ b/halfsiphash.c
@@ -70,8 +70,8 @@ int halfsiphash(const uint8_t *in, const size_t inlen, const uint8_t *k,
     assert((outlen == 4) || (outlen == 8));
     uint32_t v0 = 0;
     uint32_t v1 = 0;
-    uint32_t v2 = 0x6c796765;
-    uint32_t v3 = 0x74656462;
+    uint32_t v2 = UINT32_C(0x6c796765);
+    uint32_t v3 = UINT32_C(0x74656462);
     uint32_t k0 = U8TO32_LE(k);
     uint32_t k1 = U8TO32_LE(k + 4);
     uint32_t m;
diff --git a/siphash.c b/siphash.c
index d69f4b5..41c6f50 100644
--- a/siphash.c
+++ b/siphash.c
@@ -79,10 +79,10 @@ int siphash(const uint8_t *in, const size_t inlen, const uint8_t *k,
             uint8_t *out, const size_t outlen) {
 
     assert((outlen == 8) || (outlen == 16));
-    uint64_t v0 = 0x736f6d6570736575ULL;
-    uint64_t v1 = 0x646f72616e646f6dULL;
-    uint64_t v2 = 0x6c7967656e657261ULL;
-    uint64_t v3 = 0x7465646279746573ULL;
+    uint64_t v0 = UINT64_C(0x736f6d6570736575);
+    uint64_t v1 = UINT64_C(0x646f72616e646f6d);
+    uint64_t v2 = UINT64_C(0x6c7967656e657261);
+    uint64_t v3 = UINT64_C(0x7465646279746573);
     uint64_t k0 = U8TO64_LE(k);
     uint64_t k1 = U8TO64_LE(k + 8);
     uint64_t m;