diff --git a/sys/hashes/sha224.c b/sys/hashes/sha224.c
index 4bc4c7ed3985..3a9cedb736ad 100644
--- a/sys/hashes/sha224.c
+++ b/sys/hashes/sha224.c
@@ -40,18 +40,12 @@ void sha224_init(sha224_context_t *ctx)
     ctx->state[7] = 0xBEFA4FA4;
 }
 
-void *sha224(const void *data, size_t len, void *digest)
+void sha224(const void *data, size_t len, void *digest)
 {
     sha224_context_t c;
-    static unsigned char m[SHA224_DIGEST_LENGTH];
-
-    if (digest == NULL) {
-        digest = m;
-    }
+    assert(digest);
 
     sha224_init(&c);
     sha224_update(&c, data, len);
     sha224_final(&c, digest);
-
-    return digest;
 }
diff --git a/sys/include/hashes/sha224.h b/sys/include/hashes/sha224.h
index ecfb1fc64c2b..678308af5f6d 100644
--- a/sys/include/hashes/sha224.h
+++ b/sys/include/hashes/sha224.h
@@ -114,7 +114,7 @@ static inline void sha224_final(sha224_context_t *ctx, void *digest)
  *                    be SHA224_DIGEST_LENGTH
  *                    if digest == NULL, one static buffer is used
  */
-void *sha224(const void *data, size_t len, void *digest);
+void sha224(const void *data, size_t len, void *digest);
 
 #ifdef __cplusplus
 }