diff --git a/sys/hashes/sha512_common.c b/sys/hashes/sha512_common.c
index b205c1e746b2..b5480d824cf0 100644
--- a/sys/hashes/sha512_common.c
+++ b/sys/hashes/sha512_common.c
@@ -164,6 +164,8 @@ static const unsigned char PAD[128] = {
 /* Add padding and terminating bit-count. */
 void sha512_common_pad(sha512_common_context_t *ctx)
 {
+    assert(ctx != NULL);
+
     /*
      * Convert length to a vector of bytes -- we do this now rather
      * than later because the length will change after we pad.
@@ -184,6 +186,8 @@ void sha512_common_pad(sha512_common_context_t *ctx)
 /* Add bytes into the hash */
 void sha512_common_update(sha512_common_context_t *ctx, const void *data, size_t len)
 {
+    assert(ctx != NULL);
+
     /* Number of bytes left in the buffer from previous updates */
     uint8_t r = (ctx->count[1] >> 3) & 0x7f;
     /* Number of bytes free in the buffer from previous updates */
@@ -233,6 +237,8 @@ void sha512_common_update(sha512_common_context_t *ctx, const void *data, size_t
  */
 void sha512_common_final(sha512_common_context_t *ctx, void *dst, size_t dig_len)
 {
+    assert(ctx != NULL);
+
     /* Add padding */
     sha512_common_pad(ctx);
 
diff --git a/sys/include/hashes/sha512.h b/sys/include/hashes/sha512.h
index f632904c9b29..4777b7eec9f3 100644
--- a/sys/include/hashes/sha512.h
+++ b/sys/include/hashes/sha512.h
@@ -49,14 +49,14 @@ typedef sha512_common_context_t sha512_context_t;
 /**
  * @brief SHA-512 initialization.  Begins a SHA-512 operation.
  *
- * @param ctx  sha512_context_t handle to init
+ * @param ctx  sha512_context_t handle to init, must not be NULL
  */
 void sha512_init(sha512_context_t *ctx);
 
 /**
  * @brief Add bytes into the hash
  *
- * @param ctx      sha512_context_t handle to use
+ * @param ctx      sha512_context_t handle to use, must not be NULL
  * @param[in] data Input data
  * @param[in] len  Length of @p data
  */
@@ -69,7 +69,7 @@ static inline void sha512_update(sha512_context_t *ctx, const void *data, size_t
  * @brief SHA-512 finalization.  Pads the input data, exports the hash value,
  * and clears the context state.
  *
- * @param ctx           sha512_context_t handle to use
+ * @param ctx           sha512_context_t handle to use, must not be NULL
  * @param[out] digest   pointer to resulting digest, this is the hash of all the bytes.
  *                      Length must be at least SHA512_DIGEST_LENGTH
  */
diff --git a/sys/include/hashes/sha512_common.h b/sys/include/hashes/sha512_common.h
index d00e40843006..347b6cdfe38f 100644
--- a/sys/include/hashes/sha512_common.h
+++ b/sys/include/hashes/sha512_common.h
@@ -43,14 +43,14 @@ typedef struct {
 /**
  * @brief SHA-512 initialization.  Begins a SHA-512 operation.
  *
- * @param ctx  sha512_common_context_t handle to init
+ * @param ctx  sha512_common_context_t handle to init, must not be NULL
  */
 void sha512_common_pad(sha512_common_context_t *ctx);
 
 /**
  * @brief Add bytes into the hash
  *
- * @param ctx      sha512_common_context_t handle to use
+ * @param ctx      sha512_common_context_t handle to use, must not be NULL
  * @param[in] data Input data
  * @param[in] len  Length of @p data
  */
@@ -60,7 +60,7 @@ void sha512_common_update(sha512_common_context_t *ctx, const void *data, size_t
  * @brief SHA-512 finalization.  Pads the input data, exports the hash value,
  * and clears the context state.
  *
- * @param ctx           sha512_common_context_t handle to use
+ * @param ctx           sha512_common_context_t handle to use, must not be NULL
  * @param[out] digest   resulting digest, this is the hash of all the bytes
  * @param[in] dig_len   Length of @p digest
  */