diff --git a/src/uuid4.c b/src/uuid4.c
index 2263916..35bb483 100644
--- a/src/uuid4.c
+++ b/src/uuid4.c
@@ -27,7 +27,7 @@ int main(void) {
 UUID4 gen_uuid4(XOR256State *state) {
   UUID4 uuid = { .high = wapp_xorshift_256_generate(state), .low = wapp_xorshift_256_generate(state) };
   uuid.high = (uuid.high & 0xffffffffffff0fff) | 0x0000000000004000;
-  uuid.low  = (uuid.low  & 0xbfffffffffffffff) | 0x8000000000000000;
+  uuid.low  = (uuid.low  & 0x3fffffffffffffff) | 0x8000000000000000;
   return uuid;
 }