diff --git a/ChangeLog b/ChangeLog
index fb31153f04..898c5d096b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -38,6 +38,7 @@ Changes in version 0.2.0.20-?? - 2008-02-??
       cached-descriptors file. Patch by freddy77; bugfix on 0.1.2.
     - Make the new hidden service code respect the SafeLogging setting.
       Bugfix on 0.2.0.x.  Patch from Karsten.
+    - Detect size overflow in zlib code.
 
   o Code simplifications and refactoring:
     - Remove the tor_strpartition function: its logic was confused,
diff --git a/src/common/container.c b/src/common/container.c
index 5ac16bdb1b..6bd8df689d 100644
--- a/src/common/container.c
+++ b/src/common/container.c
@@ -66,6 +66,8 @@ smartlist_set_capacity(smartlist_t *sl, int n)
 {
   if (n < sl->num_used)
     n = sl->num_used;
+  if (n < 1)
+    n = 1;
   if (sl->capacity != n) {
     sl->capacity = n;
     sl->list = tor_realloc(sl->list, sizeof(void*)*sl->capacity);
diff --git a/src/common/torgzip.c b/src/common/torgzip.c
index 1ce77cb61d..40c01ba682 100644
--- a/src/common/torgzip.c
+++ b/src/common/torgzip.c
@@ -71,7 +71,7 @@ tor_gzip_compress(char **out, size_t *out_len,
                   compress_method_t method)
 {
   struct z_stream_s *stream = NULL;
-  size_t out_size;
+  size_t out_size, old_size;
   off_t offset;
 
   tor_assert(out);
@@ -119,7 +119,12 @@ tor_gzip_compress(char **out, size_t *out_len,
           break;
       case Z_BUF_ERROR:
         offset = stream->next_out - ((unsigned char*)*out);
+        old_size = out_size;
         out_size *= 2;
+        if (out_size < old_size) {
+          log_warn(LD_GENERAL, "Size overflow in compression.");
+          goto err;
+        }
         *out = tor_realloc(*out, out_size);
         stream->next_out = (unsigned char*)(*out + offset);
         if (out_size - offset > UINT_MAX) {
@@ -178,7 +183,7 @@ tor_gzip_uncompress(char **out, size_t *out_len,
                     int protocol_warn_level)
 {
   struct z_stream_s *stream = NULL;
-  size_t out_size;
+  size_t out_size, old_size;
   off_t offset;
   int r;
 
@@ -245,7 +250,12 @@ tor_gzip_uncompress(char **out, size_t *out_len,
           goto err;
         }
         offset = stream->next_out - (unsigned char*)*out;
+        old_size = out_size;
         out_size *= 2;
+        if (out_size < old_size) {
+          log_warn(LD_GENERAL, "Size overflow in compression.");
+          goto err;
+        }
         *out = tor_realloc(*out, out_size);
         stream->next_out = (unsigned char*)(*out + offset);
         if (out_size - offset > UINT_MAX) {