diff --git a/imap/http_dav.c b/imap/http_dav.c
index d5f7c114a2..abc6da42ca 100644
--- a/imap/http_dav.c
+++ b/imap/http_dav.c
@@ -6108,7 +6108,7 @@ EXPORTED int meth_propfind(struct transaction_t *txn, void *params)
     xmlDocPtr indoc = NULL, outdoc = NULL;
     xmlNodePtr root, cur = NULL, props = NULL;
     xmlNsPtr ns[NUM_NAMESPACE];
-    struct hash_table ns_table = { 0, NULL, NULL };
+    struct hash_table ns_table = HASH_TABLE_INITIALIZER;
     struct propfind_ctx fctx;
 
     memset(&fctx, 0, sizeof(struct propfind_ctx));
@@ -8083,7 +8083,7 @@ int meth_report(struct transaction_t *txn, void *params)
     xmlNodePtr inroot = NULL, outroot = NULL, cur, prop = NULL, props = NULL;
     const struct report_type_t *report = NULL;
     xmlNsPtr ns[NUM_NAMESPACE];
-    struct hash_table ns_table = { 0, NULL, NULL };
+    struct hash_table ns_table = HASH_TABLE_INITIALIZER;
     struct propfind_ctx fctx;
 
     memset(&fctx, 0, sizeof(struct propfind_ctx));
diff --git a/imap/jmap_mail.c b/imap/jmap_mail.c
index 7f2d9cb563..84845d273b 100644
--- a/imap/jmap_mail.c
+++ b/imap/jmap_mail.c
@@ -4334,7 +4334,7 @@ static void _email_querychanges_collapsed(jmap_req_t *req,
     memset(&touched_ids, 0, sizeof(hash_table));
     construct_hash_table(&touched_ids, mdcount + 1, 0);
 
-    hashu64_table touched_cids = HASH_TABLE_INITIALIZER;
+    hashu64_table touched_cids = HASHU64_TABLE_INITIALIZER;
     memset(&touched_cids, 0, sizeof(hashu64_table));
     construct_hashu64_table(&touched_cids, mdcount + 1, 0);
 
diff --git a/lib/hash.c b/lib/hash.c
index 639b6997e6..593f1bf968 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -43,10 +43,11 @@ EXPORTED hash_table *construct_hash_table(hash_table *table, size_t size, int us
       assert(table);
       assert(size);
 
-      table->size  = size;
+      table->size = size;
+      table->seed = rand(); /* might be zero, that's okay */
 
       /* Allocate the table -- different for using memory pools and not */
-      if(use_mpool) {
+      if (use_mpool) {
           /* Allocate an initial memory pool for 32 byte keys + the hash table
            * + the buckets themselves */
           table->pool =
@@ -72,7 +73,7 @@ EXPORTED hash_table *construct_hash_table(hash_table *table, size_t size, int us
 
 EXPORTED void *hash_insert(const char *key, void *data, hash_table *table)
 {
-      unsigned val = strhash(key) % table->size;
+      unsigned val = strhash_seeded(table->seed, key) % table->size;
       bucket *ptr, *newptr;
       bucket **prev;
 
@@ -159,7 +160,7 @@ EXPORTED void *hash_lookup(const char *key, hash_table *table)
       if (!table->size)
           return NULL;
 
-      val = strhash(key) % table->size;
+      val = strhash_seeded(table->seed, key) % table->size;
 
       if (!(table->table)[val])
             return NULL;
@@ -183,7 +184,7 @@ EXPORTED void *hash_lookup(const char *key, hash_table *table)
  * since it will leak memory until you get rid of the entire hash table */
 EXPORTED void *hash_del(const char *key, hash_table *table)
 {
-      unsigned val = strhash(key) % table->size;
+      unsigned val = strhash_seeded(table->seed, key) % table->size;
       bucket *ptr, *last = NULL;
 
       if (!(table->table)[val])
diff --git a/lib/hash.h b/lib/hash.h
index e49037d614..e476de77da 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -3,10 +3,11 @@
 #define HASH__H
 
 #include <stddef.h>           /* For size_t     */
+#include <stdint.h>
 #include "mpool.h"
 #include "strarray.h"
 
-#define HASH_TABLE_INITIALIZER {0, NULL, NULL}
+#define HASH_TABLE_INITIALIZER {0, 0, NULL, NULL}
 
 /*
 ** A hash table consists of an array of these buckets.  Each bucket
@@ -32,6 +33,7 @@ typedef struct bucket {
 
 typedef struct hash_table {
     size_t size;
+    uint32_t seed;
     bucket **table;
     struct mpool *pool;
 } hash_table;
diff --git a/lib/strhash.c b/lib/strhash.c
index d7c1741d2a..1b3251db73 100644
--- a/lib/strhash.c
+++ b/lib/strhash.c
@@ -42,17 +42,32 @@
 
 #include "config.h"
 
-EXPORTED unsigned strhash(const char *string)
+#include "lib/strhash.h"
+
+/* The well-known djb2 algorithm (e.g. http://www.cse.yorku.ca/~oz/hash.html),
+ * with the addition of an optional seed to limit predictability.
+ *
+ * XXX return type 'unsigned' for back-compat to previous version, but
+ * XXX ought to be 'uint32_t'
+ */
+EXPORTED unsigned strhash_seeded_djb2(uint32_t seed, const char *string)
 {
-      unsigned ret_val = 0;
-      int i;
+    const unsigned char *ustr = (const unsigned char *) string;
+    unsigned hash = 5381;
+    int c;
 
-      while (*string)
-      {
-            i = (int) *string;
-            ret_val ^= i;
-            ret_val <<= 1;
-            string ++;
-      }
-      return ret_val;
+    if (seed) {
+        /* treat the bytes of the seed as a prefix to the string */
+        unsigned i;
+        for (i = 0; i < sizeof seed; i++) {
+            c = seed & 0xff;
+            hash = ((hash << 5) + hash) ^ c;
+            seed >>= 8;
+        }
+    }
+
+    while ((c = *ustr++))
+        hash = ((hash << 5) + hash) ^ c;
+
+    return hash;
 }
diff --git a/lib/strhash.h b/lib/strhash.h
index 34533fdffa..27339bb288 100644
--- a/lib/strhash.h
+++ b/lib/strhash.h
@@ -41,7 +41,11 @@
  */
 
 #ifndef _STRHASH_H_
+#include <stdint.h>
 
-unsigned strhash(const char *string);
+unsigned strhash_seeded_djb2(uint32_t seed, const char *string);
+
+#define strhash(in)             strhash_seeded_djb2((0),  (in))
+#define strhash_seeded(sd, in)  strhash_seeded_djb2((sd), (in))
 
 #endif /* _STRHASH_H_ */