diff --git a/drivers/char/random.c b/drivers/char/random.c
index 844474b8319e..402e3ac7f4a9 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -358,16 +358,6 @@
 
 /* #define ADD_INTERRUPT_BENCH */
 
-/*
- * To allow fractional bits to be tracked, the entropy_count field is
- * denominated in units of 1/8th bits.
- *
- * 2*(POOL_ENTROPY_SHIFT + poolbitshift) must <= 31, or the multiply in
- * credit_entropy_bits() needs to be 64 bits wide.
- */
-#define POOL_ENTROPY_SHIFT 3
-#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT)
-
 /*
  * If the entropy count falls under this number of bits, then we
  * should wake up processes which are selecting or polling on write
@@ -425,8 +415,13 @@ enum poolinfo {
 	POOL_WORDMASK = POOL_WORDS - 1,
 	POOL_BYTES = POOL_WORDS * sizeof(u32),
 	POOL_BITS = POOL_BYTES * 8,
-	POOL_BITSHIFT = ilog2(POOL_WORDS) + 5,
-	POOL_FRACBITS = POOL_WORDS << (POOL_ENTROPY_SHIFT + 5),
+	POOL_BITSHIFT = ilog2(POOL_BITS),
+
+	/* To allow fractional bits to be tracked, the entropy_count field is
+	 * denominated in units of 1/8th bits. */
+	POOL_ENTROPY_SHIFT = 3,
+#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT)
+	POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT,
 
 	/* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
 	POOL_TAP1 = 104,
@@ -652,6 +647,9 @@ static void credit_entropy_bits(int nbits)
 	int entropy_count, entropy_bits, orig;
 	int nfrac = nbits << POOL_ENTROPY_SHIFT;
 
+	/* Ensure that the multiplication can avoid being 64 bits wide. */
+	BUILD_BUG_ON(2 * (POOL_ENTROPY_SHIFT + POOL_BITSHIFT) > 31);
+
 	if (!nbits)
 		return;
 
@@ -687,13 +685,13 @@ retry:
 		/* The +2 corresponds to the /4 in the denominator */
 
 		do {
-			unsigned int anfrac = min(pnfrac, POOL_FRACBITS/2);
+			unsigned int anfrac = min(pnfrac, POOL_FRACBITS / 2);
 			unsigned int add =
-				((POOL_FRACBITS - entropy_count)*anfrac*3) >> s;
+				((POOL_FRACBITS - entropy_count) * anfrac * 3) >> s;
 
 			entropy_count += add;
 			pnfrac -= anfrac;
-		} while (unlikely(entropy_count < POOL_FRACBITS-2 && pnfrac));
+		} while (unlikely(entropy_count < POOL_FRACBITS - 2 && pnfrac));
 	}
 
 	if (WARN_ON(entropy_count < 0)) {