--- a/lib/freebl/blapi.h
+++ b/lib/freebl/blapi.h
@@ -1464,16 +1464,22 @@ FIPS186Change_GenerateX(unsigned char *X
  *        q, DSA_SUBPRIME_LEN bytes
  * Output: xj, DSA_SUBPRIME_LEN bytes
  */
 extern SECStatus
 FIPS186Change_ReduceModQForDSA(const unsigned char *w,
                                const unsigned char *q,
                                unsigned char *xj);
 
+/* To allow NIST KAT tests */
+extern SECStatus
+PRNGTEST_Instantiate_Kat(const PRUint8 *entropy, unsigned int entropy_len,
+                         const PRUint8 *nonce, unsigned int nonce_len,
+                         const PRUint8 *personal_string, unsigned int ps_len);
+
 /*
  * The following functions are for FIPS poweron self test and FIPS algorithm
  * testing.
  */
 extern SECStatus
 PRNGTEST_Instantiate(const PRUint8 *entropy, unsigned int entropy_len,
                      const PRUint8 *nonce, unsigned int nonce_len,
                      const PRUint8 *personal_string, unsigned int ps_len);

--- a/lib/freebl/drbg.c
+++ b/lib/freebl/drbg.c
@@ -94,17 +94,18 @@ struct RNGContextStr {
                                               * save the rest of the rng output for
                                               * another partial block */
     PRUint8 dataAvail;                       /* # bytes of output available in our cache,
                                               * [0...SHA256_LENGTH] */
     /* store additional data that has been shovelled off to us by
      * RNG_RandomUpdate. */
     PRUint8 additionalDataCache[PRNG_ADDITONAL_DATA_CACHE_SIZE];
     PRUint32 additionalAvail;
-    PRBool isValid; /* false if RNG reaches an invalid state */
+    PRBool isValid;   /* false if RNG reaches an invalid state */
+    PRBool isKatTest; /* true if running NIST PRNG KAT tests */
 };
 
 typedef struct RNGContextStr RNGContext;
 static RNGContext *globalrng = NULL;
 static RNGContext theGlobalRng;
 
 /*
  * The next several functions are derived from the NIST SP 800-90
@@ -145,27 +146,29 @@ prng_Hash_df(PRUint8 *requested_bytes, u
                    no_of_bytes_to_return);
         requested_bytes += hash_return_len;
         no_of_bytes_to_return -= hash_return_len;
     }
     return SECSuccess;
 }
 
 /*
- * Hash_DRBG Instantiate NIST SP 800-80 10.1.1.2
+ * Hash_DRBG Instantiate NIST SP 800-90 10.1.1.2
  *
  * NOTE: bytes & len are entropy || nonce || personalization_string. In
  * normal operation, NSS calculates them all together in a single call.
  */
 static SECStatus
 prng_instantiate(RNGContext *rng, const PRUint8 *bytes, unsigned int len)
 {
-    if (len < PRNG_SEEDLEN) {
-        /* if the seedlen is to small, it's probably because we failed to get
-     * enough random data */
+    if (!rng->isKatTest && len < PRNG_SEEDLEN) {
+        /* If the seedlen is too small, it's probably because we failed to get
+         * enough random data.
+         * This is stricter than NIST SP800-90A requires. Don't enforce it for
+         * tests. */
         PORT_SetError(SEC_ERROR_NEED_RANDOM);
         return SECFailure;
     }
     prng_Hash_df(V(rng), VSize(rng), bytes, len, NULL, 0);
     rng->V_type = prngCGenerateType;
     prng_Hash_df(rng->C, sizeof rng->C, rng->V_Data, sizeof rng->V_Data, NULL, 0);
     PRNG_RESET_RESEED_COUNT(rng)
     return SECSuccess;
@@ -267,17 +270,17 @@ prng_reseed_test(RNGContext *rng, const 
             carry += dest[k1] + add[k2];                             \
             dest[k1] = (PRUint8)carry;                               \
             carry >>= 8;                                             \
         }                                                            \
     }
 
 #define PRNG_ADD_BITS_AND_CARRY(dest, dest_len, add, len, carry) \
     PRNG_ADD_BITS(dest, dest_len, add, len, carry)               \
-    PRNG_ADD_CARRY_ONLY(dest, dest_len - len, carry)
+    PRNG_ADD_CARRY_ONLY(dest, dest_len - len - 1, carry)
 
 /*
  * This function expands the internal state of the prng to fulfill any number
  * of bytes we need for this request. We only use this call if we need more
  * than can be supplied by a single call to SHA256_HashBuf.
  *
  * This function is specified in NIST SP 800-90 section 10.1.1.4, Hashgen
  */
@@ -436,16 +439,17 @@ rng_init(void)
             return PR_FAILURE;
         }
 
         if (rv != SECSuccess) {
             return PR_FAILURE;
         }
         /* the RNG is in a valid state */
         globalrng->isValid = PR_TRUE;
+        globalrng->isKatTest = PR_FALSE;
 
         /* fetch one random value so that we can populate rng->oldV for our
          * continous random number test. */
         prng_generateNewBytes(globalrng, bytes, SHA256_LENGTH, NULL, 0);
 
         /* Fetch more entropy into the PRNG */
         RNG_SystemInfoForRNG();
     }
@@ -691,16 +695,27 @@ RNG_RNGShutdown(void)
 /*
  * Test case interface. used by fips testing and power on self test
  */
 /* make sure the test context is separate from the global context, This
   * allows us to test the internal random number generator without losing
   * entropy we may have previously collected. */
 RNGContext testContext;
 
+SECStatus
+PRNGTEST_Instantiate_Kat(const PRUint8 *entropy, unsigned int entropy_len,
+                         const PRUint8 *nonce, unsigned int nonce_len,
+                         const PRUint8 *personal_string, unsigned int ps_len)
+{
+    testContext.isKatTest = PR_TRUE;
+    return PRNGTEST_Instantiate(entropy, entropy_len,
+                                nonce, nonce_len,
+                                personal_string, ps_len);
+}
+
 /*
  * Test vector API. Use NIST SP 800-90 general interface so one of the
  * other NIST SP 800-90 algorithms may be used in the future.
  */
 SECStatus
 PRNGTEST_Instantiate(const PRUint8 *entropy, unsigned int entropy_len,
                      const PRUint8 *nonce, unsigned int nonce_len,
                      const PRUint8 *personal_string, unsigned int ps_len)