It's not surprising, and it is not peculiar to FNV-1a. Most of these hashes will exhibit this same behavior. Since the hash iterates over the characters in the

It's not surprising, and it is not peculiar to FNV-1a. Most of these hashes will exhibit this same behavior. Since the hash iterates over the characters in the string, once you find two colliding strings S and T, if you append any other string to both S and T, the hashes of S' and T' will also be identical. Try it yourself: #include <stdio.h> #include "hash_32a.c" int main(int argc, char* argv[]) { const char* s[] = { "altarage", "zinke", "altarage_foo", "zinke_foo", "altarage_xyzzy", "zinke_xyzzy" }; int i; for (i = 0; i < sizeof s / sizeof (char*); ++i) { Fnv32_t x = fnv_32a_str(s[i], FNV1_32A_INIT); printf("%s: %08x\n", s[i], x); } } $ ./test_fnv1a altarage: e460d8b6 zinke: e460d8b6 altarage_foo: 3d8619c5 zinke_foo: 3d8619c5 altarage_xyzzy: 2a6373cf zinke_xyzzy: 2a6373cf