1 files changed, 6 insertions, 4 deletions

diff --git a/gzread.c b/gzread.c
index 2d4ca42..d2ab6b1 100644
--- a/gzread.c
+++ b/gzread.c
@@ -50,10 +50,12 @@ local int gz_avail(gz_statep state) {
         if (strm->avail_in) {       /* copy what's there to the start */
             unsigned char *p = state->in;
             unsigned const char *q = strm->next_in;
-            unsigned n = strm->avail_in;
-            do {
-                *p++ = *q++;
-            } while (--n);
+            if (q != p) {
+                unsigned n = strm->avail_in;
+                do {
+                    *p++ = *q++;
+                } while (--n);
+            }
         }
         if (gz_load(state, state->in + strm->avail_in,
                     state->size - strm->avail_in, &got) == -1)