--- a/src/random.h
+++ b/src/random.h
@@ -16,8 +16,8 @@
 const int N = 624;
 const int M = 397;
 const unsigned int MATRIX_A = 0x9908b0df; /* constant vector a */
-const int UPPER_MASK = 0x80000000; /* most significant w-r bits */
-const int LOWER_MASK = 0x7fffffff; /* least significant r bits */
+const unsigned int UPPER_MASK = 0x80000000; /* most significant w-r bits */
+const unsigned int LOWER_MASK = 0x7fffffff; /* least significant r bits */
 
 static unsigned int mt[N]; /* the array for the state vector  */
 static int mti=N+1; /* mti==N+1 means mt[N] is not initialized */