diff --git a/dtls_prng.h b/dtls_prng.h
index c445c80d..af02e827 100644
--- a/dtls_prng.h
+++ b/dtls_prng.h
@@ -37,10 +37,10 @@
  * implementation for prng().  You might want to change prng() to use
  * a better PRNG on your specific platform.
  *
- * @param buf The buffer to fill
- * @param len the length of the buffer to fill
+ * @param buf The buffer to fill.
+ * @param len the length of the buffer to fill.
  *
- * @return 1 buffer filled
+ * @return 1 buffer filled, else 0 on error.
  */
 int dtls_prng(unsigned char *buf, size_t len);
 
diff --git a/platform-specific/dtls_prng_contiki.c b/platform-specific/dtls_prng_contiki.c
index 4730f77b..48befb30 100644
--- a/platform-specific/dtls_prng_contiki.c
+++ b/platform-specific/dtls_prng_contiki.c
@@ -27,11 +27,12 @@ int
 dtls_prng(unsigned char *buf, size_t len)
 {
 #ifdef HAVE_PRNG
+  /* contiki_prng_impl() must return 0 on failure, else 1. */
   return contiki_prng_impl(buf, len);
 #else /* ! HAVE_PRNG */
   /**
    * Fills \p buf with \p len random bytes. This is the default
-   * implementation for prng().  You might want to change prng() to use
+   * implementation for dtls_prng().  You might want to change dtls_prng() to use
    * a better PRNG on your specific platform.
    */
   unsigned short v = random_rand();
@@ -43,7 +44,7 @@ dtls_prng(unsigned char *buf, size_t len)
   }
 
   memcpy(buf, &v, len);
-  return len;
+  return 1;
 }
 #endif /* ! HAVE_PRNG */
 
diff --git a/platform-specific/dtls_prng_espidf.c b/platform-specific/dtls_prng_espidf.c
index 084bcecb..c342b516 100644
--- a/platform-specific/dtls_prng_espidf.c
+++ b/platform-specific/dtls_prng_espidf.c
@@ -26,13 +26,13 @@
 
 /**
  * Fills \p buf with \p len random bytes. This is the default
- * implementation for prng().  You might want to change prng() to use
+ * implementation for dtls_prng().  You might want to change dtls_prng() to use
  * a better PRNG on your specific platform.
  */
 int
 dtls_prng(unsigned char *buf, size_t len) {
   esp_fill_random(buf, len);
-  return len;
+  return 1;
 }
 
 void
diff --git a/platform-specific/dtls_prng_lwip.c b/platform-specific/dtls_prng_lwip.c
index 40ad3ef0..192750c8 100644
--- a/platform-specific/dtls_prng_lwip.c
+++ b/platform-specific/dtls_prng_lwip.c
@@ -22,7 +22,6 @@
 int
 dtls_prng(unsigned char *buf, size_t len) {
   u32_t v = LWIP_RAND();
-  size_t k_len = len;
 
   while (len > sizeof(v)) {
     memcpy(buf, &v, sizeof(v));
@@ -32,7 +31,7 @@ dtls_prng(unsigned char *buf, size_t len) {
   }
 
   memcpy(buf, &v, len);
-  return k_len;
+  return 1;
 }
 
 void
diff --git a/platform-specific/dtls_prng_posix.c b/platform-specific/dtls_prng_posix.c
index 2c3f3e71..ebb22b44 100644
--- a/platform-specific/dtls_prng_posix.c
+++ b/platform-specific/dtls_prng_posix.c
@@ -36,13 +36,13 @@
 
 /**
  * Fills @p buf with @p len random bytes. This is the default
- * implementation for prng().  You might want to change prng() to use
+ * implementation for dtls_prng().  You might want to change dtls_prng() to use
  * a better PRNG on your specific platform.
  */
 int
 dtls_prng(unsigned char *buf, size_t len) {
 #ifdef HAVE_GETRANDOM
-  return getrandom(buf, len, 0);
+  return getrandom(buf, len, 0) > 0 ? 1 : 0;
 #elif defined(HAVE_RANDOM)
 
 #define RAND_BYTES (RAND_MAX >= 0xffffff ? 3 : (RAND_MAX >= 0xffff ? 2 : 1))
@@ -64,14 +64,13 @@ dtls_prng(unsigned char *buf, size_t len) {
       }
     }
   }
-  return len;
+  return 1;
 #else /*!HAVE_GETRANDOM && !HAVE_RANDOM */
   #error "CVE-2021-34430: using rand() for crypto randoms is not secure!"
   #error "Please update you C-library and rerun the auto-configuration."
-  size_t klen = len;
   while (len--)
     *buf++ = rand() & 0xFF;
-  return klen;
+  return 1;
 #endif /* !HAVE_GETRANDOM */
 }
 
diff --git a/platform-specific/dtls_prng_riot.c b/platform-specific/dtls_prng_riot.c
index 3a03b7ff..6bfa1ec3 100644
--- a/platform-specific/dtls_prng_riot.c
+++ b/platform-specific/dtls_prng_riot.c
@@ -25,7 +25,7 @@
 int
 dtls_prng(unsigned char *buf, size_t len) {
   random_bytes(buf, len);
-  return len;
+  return 1;
 }
 
 void
diff --git a/platform-specific/dtls_prng_win.c b/platform-specific/dtls_prng_win.c
index a71633b2..287a5b8b 100644
--- a/platform-specific/dtls_prng_win.c
+++ b/platform-specific/dtls_prng_win.c
@@ -30,16 +30,16 @@ int
 dtls_prng(unsigned char *buf, size_t len) {
   errno_t err;
   unsigned int number;
-  size_t klen = len;
+
   while (len--) {
     err = rand_s(&number);
     if (err != 0) {
       dtls_emerg("PRNG failed\n");
-      return err;
+      return 0;
     }
     *buf++ = number & 0xFF;
   }
-  return klen;
+  return 1;
 }
 
 void
diff --git a/platform-specific/dtls_prng_zephyr.c b/platform-specific/dtls_prng_zephyr.c
index b9576378..245c97b8 100644
--- a/platform-specific/dtls_prng_zephyr.c
+++ b/platform-specific/dtls_prng_zephyr.c
@@ -30,8 +30,7 @@
 
 int
 dtls_prng(unsigned char *buf, size_t len) {
-  sys_csrand_get(buf, len);
-  return len;
+  return sys_csrand_get(buf, len) == 0 ? 1 : 0;
 }
 
 void
diff --git a/tests/unit-tests/test_ecc.c b/tests/unit-tests/test_ecc.c
index a2dc99fe..5476b54b 100644
--- a/tests/unit-tests/test_ecc.c
+++ b/tests/unit-tests/test_ecc.c
@@ -132,10 +132,10 @@ t_test_ecc_dh(void) {
   int ret;
 
   ret = dtls_prng((void *)secretA, sizeof(secretA));
-  CU_ASSERT(ret > 1);
+  CU_ASSERT(ret == 1);
 
   ret = dtls_prng((void *)secretB, sizeof(secretB));
-  CU_ASSERT(ret > 1);
+  CU_ASSERT(ret == 1);
 
   ecc_ec_mult(BasePointx, BasePointy, secretA, tempx, tempy);
   ecc_ec_mult(BasePointx, BasePointy, secretB, tempBx1, tempBy1);