diff --git a/src/lj_jit.h b/src/lj_jit.h
index 92054e3d..4c767562 100644
--- a/src/lj_jit.h
+++ b/src/lj_jit.h
@@ -450,7 +450,7 @@ typedef struct jit_State {
 
   HotPenalty penalty[PENALTY_SLOTS];  /* Penalty slots. */
   uint32_t penaltyslot;	/* Round-robin index into penalty slots. */
-  uint32_t prngstate;	/* PRNG state. */
+  uint64_t prngstate;	/* PRNG state. */
 
 #ifdef LUAJIT_ENABLE_TABLE_BUMP
   RBCHashEntry rbchash[RBCHASH_SLOTS];  /* Reverse bytecode map. */
@@ -488,12 +488,13 @@ LJ_ALIGN(16)		/* For DISPATCH-relative addresses in assembler part. */
 #endif
 jit_State;
 
-/* Trivial PRNG e.g. used for penalty randomization. */
+/* SplitMix64 PRNG based on http://xoroshiro.di.unimi.it/splitmix64.c */
 static LJ_AINLINE uint32_t LJ_PRNG_BITS(jit_State *J, int bits)
 {
-  /* Yes, this LCG is very weak, but that doesn't matter for our use case. */
-  J->prngstate = J->prngstate * 1103515245 + 12345;
-  return J->prngstate >> (32-bits);
+  uint64_t z = (J->prngstate += UINT64_C(0x9E3779B97F4A7C15));
+  z = (z ^ (z >> 30)) * UINT64_C(0xBF58476D1CE4E5B9);
+  z = (z ^ (z >> 27)) * UINT64_C(0x94D049BB133111EB);
+  return z >> (64-bits);
 }
 
 #endif
diff --git a/src/lj_state.c b/src/lj_state.c
index 3cc0fea5..f997106c 100644
--- a/src/lj_state.c
+++ b/src/lj_state.c
@@ -225,6 +225,7 @@ LUA_API lua_State *lua_newstate(lua_Alloc f, void *ud)
     return NULL;
   }
   L->status = 0;
+  G2J(g)->prngstate = rand();
   return L;
 }