diff --git a/include/tinycrypt/ecc.h b/include/tinycrypt/ecc.h
index 6a85a5578..b6fbc6906 100644
--- a/include/tinycrypt/ecc.h
+++ b/include/tinycrypt/ecc.h
@@ -163,9 +163,9 @@ int uECC_generate_random_int(uECC_word_t *random, const uECC_word_t *top,
 
 /* uECC_RNG_Function type
  * The RNG function should fill 'size' random bytes into 'dest'. It should
- * return 1 if 'dest' was filled with random data, or 0 if the random data could
- * not be generated. The filled-in values should be either truly random, or from
- * a cryptographically-secure PRNG.
+ * return 'size' if 'dest' was filled with random data of 'size' length, or 0
+ * if the random data could not be generated. The filled-in values should be
+ * either truly random, or from a cryptographically-secure PRNG.
  *
  * A correctly functioning RNG function must be set (using uECC_set_rng())
  * before calling uECC_make_key() or uECC_sign().
@@ -181,8 +181,8 @@ typedef int(*uECC_RNG_Function)(uint8_t *dest, unsigned int size);
 
 /*
  * @brief Set the function that will be used to generate random bytes. The RNG
- * function should return 1 if the random data was generated, or 0 if the random
- * data could not be generated.
+ * function should return 'size' if the random data of length 'size' was
+ * generated, or 0 if the random data could not be generated.
  *
  * @note On platforms where there is no predefined RNG function, this must be
  * called before uECC_make_key() or uECC_sign() are used.
diff --git a/tinycrypt/ecc.c b/tinycrypt/ecc.c
index b3e3ed327..57b3228dd 100644
--- a/tinycrypt/ecc.c
+++ b/tinycrypt/ecc.c
@@ -1169,7 +1169,7 @@ int uECC_generate_random_int(uECC_word_t *random, const uECC_word_t *top,
 	}
 
 	for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
-		if (!g_rng_function((uint8_t *)random, num_words * uECC_WORD_SIZE)) {
+		if (g_rng_function((uint8_t *)random, num_words * uECC_WORD_SIZE) != num_words * uECC_WORD_SIZE) {
       			return 0;
     		}
 		random[num_words - 1] &=
diff --git a/tinycrypt/ecc_dh.c b/tinycrypt/ecc_dh.c
index ceabb0005..a63c84bba 100644
--- a/tinycrypt/ecc_dh.c
+++ b/tinycrypt/ecc_dh.c
@@ -119,7 +119,7 @@ int uECC_make_key(uint8_t *public_key, uint8_t *private_key)
 		/* Generating _private uniformly at random: */
 		uECC_RNG_Function rng_function = uECC_get_rng();
 		if (!rng_function ||
-			!rng_function((uint8_t *)_random, 2 * NUM_ECC_WORDS*uECC_WORD_SIZE)) {
+			rng_function((uint8_t *)_random, 2 * NUM_ECC_WORDS*uECC_WORD_SIZE) != 2 * NUM_ECC_WORDS*uECC_WORD_SIZE) {
         		return UECC_FAILURE;
 		}
 
diff --git a/tinycrypt/ecc_dsa.c b/tinycrypt/ecc_dsa.c
index 230f6890c..70f9c8bc6 100644
--- a/tinycrypt/ecc_dsa.c
+++ b/tinycrypt/ecc_dsa.c
@@ -151,7 +151,7 @@ int uECC_sign(const uint8_t *private_key, const uint8_t *message_hash,
 		/* Generating _random uniformly at random: */
 		uECC_RNG_Function rng_function = uECC_get_rng();
 		if (!rng_function ||
-		    !rng_function((uint8_t *)_random, 2*NUM_ECC_WORDS*uECC_WORD_SIZE)) {
+		    rng_function((uint8_t *)_random, 2*NUM_ECC_WORDS*uECC_WORD_SIZE) != 2*NUM_ECC_WORDS*uECC_WORD_SIZE) {
 			return UECC_FAILURE;
 		}