diff --git a/configure.in b/configure.in
index 6ca5531e0b..be1ee33ca2 100644
--- a/configure.in
+++ b/configure.in
@@ -158,6 +158,28 @@ AM_CONDITIONAL(NAT_PMP, test x$natpmp = xtrue)
 AM_CONDITIONAL(MINIUPNPC, test x$upnp = xtrue)
 AM_PROG_CC_C_O
 
+ifdef([AC_C_FLEXIBLE_ARRAY_MEMBER], [
+AC_C_FLEXIBLE_ARRAY_MEMBER
+], [
+ dnl Maybe we've got an old autoconf...
+ AC_CACHE_CHECK([for flexible array members],
+     tor_cv_c_flexarray,
+     [AC_COMPILE_IFELSE(
+       AC_LANG_PROGRAM([
+ struct abc { int a; char b[]; };
+], [
+ struct abc *def = malloc(sizeof(struct abc)+sizeof(char));
+ def->b[0] = 33;
+]),
+  [tor_cv_c_flexarray=yes],
+  [tor_cv_c_flexarray=no])])
+ if test $tor_cv_flexarray = yes ; then
+   AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [])
+ else
+   AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])
+ fi
+])
+
 AC_PATH_PROG([SHA1SUM], [sha1sum], none)
 AC_PATH_PROG([OPENSSL], [openssl], none)
 
diff --git a/src/common/mempool.c b/src/common/mempool.c
index c444923189..520e470c7f 100644
--- a/src/common/mempool.c
+++ b/src/common/mempool.c
@@ -137,7 +137,8 @@ struct mp_chunk_t {
   int capacity; /**< Number of items that can be fit into this chunk. */
   size_t mem_size; /**< Number of usable bytes in mem. */
   char *next_mem; /**< Pointer into part of <b>mem</b> not yet carved up. */
-  char mem[1]; /**< Storage for this chunk. (Not actual size.) */
+  /** Storage for this chunk */
+  char mem[FLEXIBLE_ARRAY_MEMBER];
 };
 
 /** Number of extra bytes needed beyond mem_size to allocate a chunk. */
diff --git a/src/or/buffers.c b/src/or/buffers.c
index 9f393b9874..48acf505ef 100644
--- a/src/or/buffers.c
+++ b/src/or/buffers.c
@@ -68,8 +68,8 @@ typedef struct chunk_t {
   size_t datalen; /**< The number of bytes stored in this chunk */
   size_t memlen; /**< The number of usable bytes of storage in <b>mem</b>. */
   char *data; /**< A pointer to the first byte of data stored in <b>mem</b>. */
-  char mem[1]; /**< The actual memory used for storage in this chunk. May be
-                * more than one byte long. */
+  char mem[FLEXIBLE_ARRAY_MEMBER]; /**< The actual memory used for storage in
+                * this chunk. */
 } chunk_t;
 
 #define CHUNK_HEADER_LEN STRUCT_OFFSET(chunk_t, mem[0])
diff --git a/src/or/connection_or.c b/src/or/connection_or.c
index 6c4f7eff2b..5b440bc7ce 100644
--- a/src/or/connection_or.c
+++ b/src/or/connection_or.c
@@ -191,7 +191,8 @@ var_cell_pack_header(const var_cell_t *cell, char *hdr_out)
 var_cell_t *
 var_cell_new(uint16_t payload_len)
 {
-  var_cell_t *cell = tor_malloc(sizeof(var_cell_t)+payload_len-1);
+  size_t size = STRUCT_OFFSET(var_cell_t, payload) + payload_len;
+  var_cell_t *cell = tor_malloc(size);
   cell->payload_len = payload_len;
   cell->command = 0;
   cell->circ_id = 0;
diff --git a/src/or/or.h b/src/or/or.h
index 2d1fbef59c..8aef2d0233 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -857,8 +857,8 @@ typedef struct cell_t {
 typedef struct var_cell_t {
   uint8_t command;
   circid_t circ_id;
-  uint16_t payload_len;
-  uint8_t payload[1];
+  uint16_t payload_len; /**< The actual length of <b>payload</b>. */
+  uint8_t payload[FLEXIBLE_ARRAY_MEMBER];
 } var_cell_t;
 
 /** A cell as packed for writing to the network. */
@@ -1660,11 +1660,11 @@ typedef struct short_policy_t {
   unsigned int is_accept : 1;
   /** The actual number of values in 'entries'. */
   unsigned int n_entries : 31;
-  /** An array of (probably more than 1!) short_policy_entry_t values,
-   * each descriping a range of ports that this policy accepts or rejects
-   * (depending on the value of is_accept).
+  /** An array of 0 or more short_policy_entry_t values, each descriping a
+   * range of ports that this policy accepts or rejects (depending on the
+   * value of is_accept).
    */
-  short_policy_entry_t entries[1];
+  short_policy_entry_t entries[FLEXIBLE_ARRAY_MEMBER];
 } short_policy_t;
 
 /** A microdescriptor is the smallest amount of information needed to build a
diff --git a/src/or/policies.c b/src/or/policies.c
index 46a431a8de..e5af7887c7 100644
--- a/src/or/policies.c
+++ b/src/or/policies.c
@@ -1382,8 +1382,8 @@ parse_short_policy(const char *summary)
   }
 
   {
-    size_t size = sizeof(short_policy_t) +
-      sizeof(short_policy_entry_t)*(n_entries-1);
+    size_t size = STRUCT_OFFSET(short_policy_t, entries) +
+      sizeof(short_policy_entry_t)*(n_entries);
     result = tor_malloc_zero(size);
 
     tor_assert( (char*)&result->entries[n_entries-1] < ((char*)result)+size);