diff --git a/sys/include/random.h b/sys/include/random.h
index 56baa9f7a6..d762149383 100644
--- a/sys/include/random.h
+++ b/sys/include/random.h
@@ -78,7 +78,7 @@ void random_init(uint32_t s);
  * slight change for C++, 2004/2/26
  *
  * @param init_key array of keys (seeds) to initialize the PRNG
- * @param key_length number of lements in init_key
+ * @param key_length number of elements in init_key
  */
 void random_init_by_array(uint32_t init_key[], int key_length);
 
diff --git a/sys/random/shaxprng.c b/sys/random/shaxprng.c
index dfbe01e2f9..f57c73c080 100644
--- a/sys/random/shaxprng.c
+++ b/sys/random/shaxprng.c
@@ -149,7 +149,7 @@ void _random_bytes(uint8_t *bytes, size_t size)
 void random_init_by_array(uint32_t init_key[], int key_length)
 {
     _shax_init(&ctx);
-    _shax_update(&ctx, init_key, key_length);
+    _shax_update(&ctx, init_key, key_length * sizeof(uint32_t));
     _shax_final(&ctx, digestdata);
 
     /* copy SHA digestdata to PRNG state */
@@ -161,7 +161,7 @@ void random_init_by_array(uint32_t init_key[], int key_length)
 
 void random_init(uint32_t seed)
 {
-    random_init_by_array((uint32_t *)&seed, sizeof(seed));
+    random_init_by_array((uint32_t *)&seed, 1);
 }
 
 uint32_t random_uint32(void)
diff --git a/tests/sys/prng_sha1prng/main.c b/tests/sys/prng_sha1prng/main.c
index 8bd4828f4d..22388668f9 100644
--- a/tests/sys/prng_sha1prng/main.c
+++ b/tests/sys/prng_sha1prng/main.c
@@ -57,7 +57,7 @@ static void test_prng_sha1prng_java_u32(void)
     /* seed the generator with 8 bytes similar to the java reference
      * implementation
      */
-    random_init_by_array(seed, sizeof(seed));
+    random_init_by_array(seed, ARRAY_SIZE(seed));
 
     /* request random samples */
     for (unsigned i = 0; i < ARRAY_SIZE(seq_seed1); i++) {