diff --git a/gzwrite.c b/gzwrite.c
index 3560193..26e89b6 100644
--- a/gzwrite.c
+++ b/gzwrite.c
@@ -444,7 +444,7 @@
         strm->avail_in = state->size;
         if (gz_comp(state, Z_NO_FLUSH) == -1)
             return state->err;
-        memcpy(state->in, state->in + state->size, left);
+        memmove(state->in, state->in + state->size, left);
         strm->next_in = state->in;
         strm->avail_in = left;
     }
@@ -543,7 +543,7 @@
         strm->avail_in = state->size;
         if (gz_comp(state, Z_NO_FLUSH) == -1)
             return state->err;
-        memcpy(state->in, state->in + state->size, left);
+        memmove(state->in, state->in + state->size, left);
         strm->next_in = state->in;
         strm->avail_in = left;
     }