diff --git a/py/binary.c b/py/binary.c
index e38aae8ea3908a5e2994ebe63986c0736d54268a..870a0942ba6f172e415110026a63c0c47d1ea3e5 100644
--- a/py/binary.c
+++ b/py/binary.c
@@ -303,7 +303,10 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **
                 // zero/sign extend if needed
                 if (BYTES_PER_WORD < 8 && size > sizeof(val)) {
                     int c = (is_signed(val_type) && (mp_int_t)val < 0) ? 0xff : 0x00;
-                    memset(p + sizeof(val), c, size - sizeof(val));
+                    memset(p, c, size);
+                    if (struct_type == '>') {
+                        p += size - sizeof(val);
+                    }
                 }
             }
     }
diff --git a/tests/basics/struct1_intbig.py b/tests/basics/struct1_intbig.py
index b1fec527ef422c060be7f69b436340e86fb0d48c..380293f36cea78a3561943887f92365af72c37c4 100644
--- a/tests/basics/struct1_intbig.py
+++ b/tests/basics/struct1_intbig.py
@@ -12,6 +12,8 @@ print(struct.pack("<I", 2**32 - 1))
 print(struct.pack("<I", 0xffffffff))
 
 # long long ints
+print(struct.pack("<Q", 1))
+print(struct.pack(">Q", 1))
 print(struct.pack("<Q", 2**64 - 1))
 print(struct.pack(">Q", 2**64 - 1))
 print(struct.pack("<Q", 0xffffffffffffffff))