diff --git a/Recipe b/Recipe
index 18f5637a..216ef967 100644
--- a/Recipe
+++ b/Recipe
@@ -239,7 +239,8 @@ pageant  : [G] winpgnt sshrsa sshpubk sshdes sshbn sshmd5 version tree234
 
 puttygen : [G] winpgen sshrsag sshdssg sshprime sshdes sshbn sshmd5 version
          + sshrand winnoise sshsha winstore misc winctrls sshrsa sshdss winmisc
-         + sshpubk sshaes sshsh512 import winutils puttygen.res tree234 LIBS
+         + sshpubk sshaes sshsh512 import winutils puttygen.res tree234
+	 + notiming LIBS
 
 pterm    : [X] UXTERM uxmisc misc ldisc settings pty uxsel BE_NONE uxstore
          + signal CHARSET cmdline ptermm version
@@ -252,7 +253,7 @@ plink    : [U] uxplink uxcons NONSSH UXSSH BE_ALL logging UXMISC signal ux_x11
 
 puttygen : [U] cmdgen sshrsag sshdssg sshprime sshdes sshbn sshmd5 version
          + sshrand uxnoise sshsha misc sshrsa sshdss uxcons uxstore uxmisc
-         + sshpubk sshaes sshsh512 import puttygen.res tree234 uxgen
+         + sshpubk sshaes sshsh512 import puttygen.res tree234 uxgen notiming
 
 pscp     : [U] scp uxsftp uxcons UXSSH BE_SSH SFTP wildcard UXMISC
 psftp    : [U] psftp uxsftp uxcons UXSSH BE_SSH SFTP UXMISC
diff --git a/be_nossh.c b/be_nossh.c
index 90ab9987..18ba32a7 100644
--- a/be_nossh.c
+++ b/be_nossh.c
@@ -31,7 +31,3 @@ void random_destroy_seed(void)
 void noise_ultralight(unsigned long data)
 {
 }
-
-void noise_regular(void)
-{
-}
diff --git a/cmdgen.c b/cmdgen.c
index 467bab62..42772aa3 100644
--- a/cmdgen.c
+++ b/cmdgen.c
@@ -616,7 +616,7 @@ int main(int argc, char **argv)
 	else
 	    strftime(default_comment, 30, "rsa-key-%Y%m%d", tm);
 
-	random_init();
+	random_ref();
 	entropy = get_random_data(bits / 8);
 	random_add_heavynoise(entropy, bits / 8);
 	memset(entropy, 0, bits/8);
diff --git a/putty.h b/putty.h
index 4ad3124a..d880dbe2 100644
--- a/putty.h
+++ b/putty.h
@@ -742,10 +742,14 @@ void luni_send(void *, wchar_t * widebuf, int len, int interactive);
  */
 
 void random_add_noise(void *noise, int length);
-void random_init(void);
 int random_byte(void);
 void random_get_savedata(void **data, int *len);
 extern int random_active;
+/* The random number subsystem is activated if at least one other entity
+ * within the program expresses an interest in it. So each SSH session
+ * calls random_ref on startup and random_unref on shutdown. */
+void random_ref(void);
+void random_unref(void);
 
 /*
  * Exports from pinger.c.
diff --git a/ssh.c b/ssh.c
index 422897f2..07d06f1f 100644
--- a/ssh.c
+++ b/ssh.c
@@ -2576,8 +2576,6 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
 
     crBegin(ssh->do_ssh1_login_crstate);
 
-    random_init();
-
     if (!pktin)
 	crWaitUntil(pktin);
 
@@ -4299,7 +4297,6 @@ static int do_ssh2_transport(Ssh ssh, unsigned char *in, int inlen,
     s->csmac_tobe = s->scmac_tobe = NULL;
     s->cscomp_tobe = s->sccomp_tobe = NULL;
 
-    random_init();
     s->first_kex = 1;
 
     {
@@ -7145,6 +7142,8 @@ static const char *ssh_init(void *frontend_handle, void **backend_handle,
     if (p != NULL)
 	return p;
 
+    random_ref();
+
     return NULL;
 }
 
@@ -7223,6 +7222,8 @@ static void ssh_free(void *handle)
     sfree(ssh);
     if (ssh->pinger)
 	pinger_free(ssh->pinger);
+
+    random_unref();
 }
 
 /*
diff --git a/sshrand.c b/sshrand.c
index a7b3dc4e..43b81234 100644
--- a/sshrand.c
+++ b/sshrand.c
@@ -5,6 +5,9 @@
 #include "putty.h"
 #include "ssh.h"
 
+/* Collect environmental noise every 5 minutes */
+#define NOISE_REGULAR_INTERVAL (5*60*TICKSPERSEC)
+
 void noise_get_heavy(void (*func) (void *, int));
 void noise_get_light(void (*func) (void *, int));
 
@@ -41,6 +44,7 @@ struct RandPool {
 
 static struct RandPool pool;
 int random_active = 0;
+long next_noise_collection;
 
 static void random_stir(void)
 {
@@ -182,16 +186,33 @@ static void random_add_heavynoise_bitbybit(void *noise, int length)
     pool.poolpos = i;
 }
 
-void random_init(void)
+static void random_timer(void *ctx, long now)
+{
+    if (random_active > 0 && now - next_noise_collection >= 0) {
+	noise_regular();
+	next_noise_collection =
+	    schedule_timer(NOISE_REGULAR_INTERVAL, random_timer, &pool);
+    }
+}
+
+void random_ref(void)
 {
     if (!random_active) {
 	memset(&pool, 0, sizeof(pool));    /* just to start with */
 
-	random_active = 1;
-
 	noise_get_heavy(random_add_heavynoise_bitbybit);
 	random_stir();
+
+	next_noise_collection =
+	    schedule_timer(NOISE_REGULAR_INTERVAL, random_timer, &pool);
     }
+
+    random_active++;
+}
+
+void random_unref(void)
+{
+    random_active--;
 }
 
 int random_byte(void)
diff --git a/windows/winpgen.c b/windows/winpgen.c
index 3f2be92e..e80dbfec 100644
--- a/windows/winpgen.c
+++ b/windows/winpgen.c
@@ -1445,7 +1445,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
             help_path = NULL;
     }
 
-    random_init();
+    random_ref();
     return DialogBox(hinst, MAKEINTRESOURCE(201), NULL,
 		     MainDlgProc) != IDOK;
 }