diff --git a/be_nos_s.c b/be_nos_s.c
index b3c61e7c..15906cfa 100644
--- a/be_nos_s.c
+++ b/be_nos_s.c
@@ -29,6 +29,6 @@ void random_destroy_seed(void)
 {
 }
 
-void noise_ultralight(unsigned long data)
+void noise_ultralight(NoiseSourceId id, unsigned long data)
 {
 }
diff --git a/be_nossh.c b/be_nossh.c
index daf15998..184f28dc 100644
--- a/be_nossh.c
+++ b/be_nossh.c
@@ -28,6 +28,6 @@ void random_destroy_seed(void)
 {
 }
 
-void noise_ultralight(unsigned long data)
+void noise_ultralight(NoiseSourceId id, unsigned long data)
 {
 }
diff --git a/putty.h b/putty.h
index 4d6a3c5b..3127c5de 100644
--- a/putty.h
+++ b/putty.h
@@ -1456,10 +1456,30 @@ FontSpec *fontspec_deserialise(BinarySource *src);
 /*
  * Exports from noise.c.
  */
+typedef enum NoiseSourceId {
+    NOISE_SOURCE_TIME,
+    NOISE_SOURCE_IOID,
+    NOISE_SOURCE_IOLEN,
+    NOISE_SOURCE_KEY,
+    NOISE_SOURCE_MOUSEBUTTON,
+    NOISE_SOURCE_MOUSEPOS,
+    NOISE_SOURCE_MEMINFO,
+    NOISE_SOURCE_STAT,
+    NOISE_SOURCE_RUSAGE,
+    NOISE_SOURCE_FGWINDOW,
+    NOISE_SOURCE_CAPTURE,
+    NOISE_SOURCE_CLIPBOARD,
+    NOISE_SOURCE_QUEUE,
+    NOISE_SOURCE_CURSORPOS,
+    NOISE_SOURCE_THREADTIME,
+    NOISE_SOURCE_PROCTIME,
+    NOISE_SOURCE_PERFCOUNT,
+    NOISE_MAX_SOURCES
+} NoiseSourceId;
 void noise_get_heavy(void (*func) (void *, int));
 void noise_get_light(void (*func) (void *, int));
 void noise_regular(void);
-void noise_ultralight(unsigned long data);
+void noise_ultralight(NoiseSourceId id, unsigned long data);
 void random_save_seed(void);
 void random_destroy_seed(void);
 
@@ -1673,7 +1693,7 @@ void luni_send(Ldisc *, const wchar_t * widebuf, int len, bool interactive);
  * Exports from sshrand.c.
  */
 
-void random_add_noise(void *noise, int length);
+void random_add_noise(NoiseSourceId source, const void *noise, int length);
 void random_read(void *buf, size_t size);
 void random_get_savedata(void **data, int *len);
 extern int random_active;
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index 7822a922..1f7f2dcc 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -987,7 +987,7 @@ gint key_event(GtkWidget *widget, GdkEventKey *event, gpointer data)
     bool generated_something = false;
     char num_keypad_key = '\0';
 
-    noise_ultralight(event->keyval);
+    noise_ultralight(NOISE_SOURCE_KEY, event->keyval);
 
 #ifdef OSX_META_KEY_CONFIG
     if (event->state & inst->system_mod_mask)
@@ -2059,7 +2059,7 @@ static gboolean button_internal(GtkFrontend *inst, GdkEventButton *event)
     /* Remember the timestamp. */
     inst->input_event_time = event->time;
 
-    noise_ultralight(event->button);
+    noise_ultralight(NOISE_SOURCE_MOUSEBUTTON, event->button);
 
     show_mouseptr(inst, true);
 
@@ -2187,7 +2187,8 @@ gint motion_event(GtkWidget *widget, GdkEventMotion *event, gpointer data)
     /* Remember the timestamp. */
     inst->input_event_time = event->time;
 
-    noise_ultralight(((uint32_t)event->x << 16) | (uint32_t)event->y);
+    noise_ultralight(NOISE_SOURCE_MOUSEPOS,
+                     ((uint32_t)event->x << 16) | (uint32_t)event->y);
 
     show_mouseptr(inst, true);
 
diff --git a/unix/uxfdsock.c b/unix/uxfdsock.c
index 6b09e6db..06a5060f 100644
--- a/unix/uxfdsock.c
+++ b/unix/uxfdsock.c
@@ -167,7 +167,7 @@ static int fdsocket_try_send(FdSocket *fds)
 
 	bufchain_prefix(&fds->pending_output_data, &data, &len);
 	ret = write(fds->outfd, data, len);
-        noise_ultralight(ret);
+        noise_ultralight(NOISE_SOURCE_IOID, ret);
 	if (ret < 0 && errno != EWOULDBLOCK) {
             if (!fds->pending_error) {
                 fds->pending_error = errno;
diff --git a/unix/uxnet.c b/unix/uxnet.c
index 910d290e..231686be 100644
--- a/unix/uxnet.c
+++ b/unix/uxnet.c
@@ -1121,7 +1121,7 @@ void try_send(NetSocket *s)
 	    bufchain_prefix(&s->output_data, &data, &len);
 	}
 	nsent = send(s->s, data, len, urgentflag);
-	noise_ultralight(nsent);
+	noise_ultralight(NOISE_SOURCE_IOLEN, nsent);
 	if (nsent <= 0) {
 	    err = (nsent < 0 ? errno : 0);
 	    if (err == EWOULDBLOCK) {
@@ -1275,7 +1275,7 @@ static void net_select_result(int fd, int event)
     if (!s)
 	return;		       /* boggle */
 
-    noise_ultralight(event);
+    noise_ultralight(NOISE_SOURCE_IOID, fd);
 
     switch (event) {
       case 4:			       /* exceptional */
@@ -1287,7 +1287,7 @@ static void net_select_result(int fd, int event)
 	     * type==2 (urgent data).
 	     */
 	    ret = recv(s->s, buf, sizeof(buf), MSG_OOB);
-	    noise_ultralight(ret);
+	    noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 	    if (ret <= 0) {
                 plug_closing(s->plug,
 			     ret == 0 ? "Internal networking trouble" :
@@ -1370,7 +1370,7 @@ static void net_select_result(int fd, int event)
 	    atmark = true;
 
 	ret = recv(s->s, buf, s->oobpending ? 1 : sizeof(buf), 0);
-	noise_ultralight(ret);
+	noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 	if (ret < 0) {
 	    if (errno == EWOULDBLOCK) {
 		break;
diff --git a/unix/uxnoise.c b/unix/uxnoise.c
index bcc78273..9b239f77 100644
--- a/unix/uxnoise.c
+++ b/unix/uxnoise.c
@@ -121,16 +121,16 @@ void noise_regular(void)
 
     if ((fd = open("/proc/meminfo", O_RDONLY)) >= 0) {
 	while ( (ret = read(fd, buf, sizeof(buf))) > 0)
-	    random_add_noise(buf, ret);
+	    random_add_noise(NOISE_SOURCE_MEMINFO, buf, ret);
 	close(fd);
     }
     if ((fd = open("/proc/stat", O_RDONLY)) >= 0) {
 	while ( (ret = read(fd, buf, sizeof(buf))) > 0)
-	    random_add_noise(buf, ret);
+	    random_add_noise(NOISE_SOURCE_STAT, buf, ret);
 	close(fd);
     }
     getrusage(RUSAGE_SELF, &rusage);
-    random_add_noise(&rusage, sizeof(rusage));
+    random_add_noise(NOISE_SOURCE_RUSAGE, &rusage, sizeof(rusage));
 }
 
 /*
@@ -138,10 +138,10 @@ void noise_regular(void)
  * will add the current time to the noise pool. It gets the scan
  * code or mouse position passed in, and adds that too.
  */
-void noise_ultralight(unsigned long data)
+void noise_ultralight(NoiseSourceId id, unsigned long data)
 {
     struct timeval tv;
     gettimeofday(&tv, NULL);
-    random_add_noise(&tv, sizeof(tv));
-    random_add_noise(&data, sizeof(data));
+    random_add_noise(NOISE_SOURCE_TIME, &tv, sizeof(tv));
+    random_add_noise(id, &data, sizeof(data));
 }
diff --git a/unix/uxpgnt.c b/unix/uxpgnt.c
index 964542a2..14e4b51b 100644
--- a/unix/uxpgnt.c
+++ b/unix/uxpgnt.c
@@ -52,7 +52,7 @@ void uxsel_input_remove(uxsel_id *id) { }
  */
 void random_save_seed(void) {}
 void random_destroy_seed(void) {}
-void noise_ultralight(unsigned long data) {}
+void noise_ultralight(NoiseSourceId id, unsigned long data) {}
 char *platform_default_s(const char *name) { return NULL; }
 bool platform_default_b(const char *name, bool def) { return def; }
 int platform_default_i(const char *name, int def) { return def; }
diff --git a/unix/uxplink.c b/unix/uxplink.c
index 385da47b..186f3a6a 100644
--- a/unix/uxplink.c
+++ b/unix/uxplink.c
@@ -958,7 +958,7 @@ int main(int argc, char **argv)
 
             if (backend_connected(backend)) {
 		ret = read(STDIN_FILENO, buf, sizeof(buf));
-                noise_ultralight(ret);
+                noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 		if (ret < 0) {
 		    perror("stdin: read");
 		    exit(1);
diff --git a/unix/uxpterm.c b/unix/uxpterm.c
index 2352b971..054d56e5 100644
--- a/unix/uxpterm.c
+++ b/unix/uxpterm.c
@@ -15,7 +15,7 @@ const bool dup_check_launchable = false; /* no need to check host name
 const bool use_pty_argv = true;
 
 /* gtkwin.c will call this, and in pterm it's not needed */
-void noise_ultralight(unsigned long data) { }
+void noise_ultralight(NoiseSourceId id, unsigned long data) { }
 
 const struct BackendVtable *select_backend(Conf *conf)
 {
diff --git a/unix/uxsel.c b/unix/uxsel.c
index cca4017c..d32eac63 100644
--- a/unix/uxsel.c
+++ b/unix/uxsel.c
@@ -115,7 +115,7 @@ void select_result(int fd, int event)
 {
     struct fd *fdstruct = find234(fds, &fd, uxsel_fd_findcmp);
 
-    noise_ultralight(fd);
+    noise_ultralight(NOISE_SOURCE_IOID, fd);
 
     /*
      * Apparently this can sometimes be NULL. Can't see how, but I
diff --git a/windows/window.c b/windows/window.c
index 0b432e88..d43afb8a 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -2696,7 +2696,7 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
 	 * Add the mouse position and message time to the random
 	 * number noise.
 	 */
-	noise_ultralight(lParam);
+	noise_ultralight(NOISE_SOURCE_MOUSEPOS, lParam);
 
 	if (wParam & (MK_LBUTTON | MK_MBUTTON | MK_RBUTTON) &&
 	    GetCapture() == hwnd) {
@@ -2724,7 +2724,7 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
 		last_mousemove = WM_NCMOUSEMOVE;
 	    }
 	}
-	noise_ultralight(lParam);
+	noise_ultralight(NOISE_SOURCE_MOUSEPOS, lParam);
 	break;
       case WM_IGNORE_CLIP:
 	ignore_clip = wParam;	       /* don't panic on DESTROYCLIPBOARD */
@@ -3179,7 +3179,7 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
 	 * Add the scan code and keypress timing to the random
 	 * number noise.
 	 */
-	noise_ultralight(lParam);
+	noise_ultralight(NOISE_SOURCE_KEY, lParam);
 
 	/*
 	 * We don't do TranslateMessage since it disassociates the
diff --git a/windows/winhandl.c b/windows/winhandl.c
index f106da7f..c2cc6a82 100644
--- a/windows/winhandl.c
+++ b/windows/winhandl.c
@@ -689,7 +689,7 @@ void handle_got_event(HANDLE event)
 	    h->u.o.sentdata(h, -h->u.o.writeerr);
 	} else {
 	    bufchain_consume(&h->u.o.queued_data, h->u.o.lenwritten);
-            noise_ultralight(h->u.o.lenwritten);
+            noise_ultralight(NOISE_SOURCE_IOLEN, h->u.o.lenwritten);
 	    h->u.o.sentdata(h, bufchain_size(&h->u.o.queued_data));
 	    handle_try_output(&h->u.o);
 	}
diff --git a/windows/winnet.c b/windows/winnet.c
index 590b98e9..0d42c989 100644
--- a/windows/winnet.c
+++ b/windows/winnet.c
@@ -1387,7 +1387,7 @@ void try_send(NetSocket *s)
 	    bufchain_prefix(&s->output_data, &data, &len);
 	}
 	nsent = p_send(s->s, data, len, urgentflag);
-	noise_ultralight(nsent);
+	noise_ultralight(NOISE_SOURCE_IOLEN, nsent);
 	if (nsent <= 0) {
 	    err = (nsent < 0 ? p_WSAGetLastError() : 0);
 	    if ((err < WSABASEERR && nsent < 0) || err == WSAEWOULDBLOCK) {
@@ -1538,7 +1538,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
 	return;
     }
 
-    noise_ultralight(lParam);
+    noise_ultralight(NOISE_SOURCE_IOID, wParam);
 
     switch (WSAGETSELECTEVENT(lParam)) {
       case FD_CONNECT:
@@ -1582,7 +1582,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
 	    atmark = true;
 
 	ret = p_recv(s->s, buf, sizeof(buf), 0);
-	noise_ultralight(ret);
+	noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 	if (ret < 0) {
 	    err = p_WSAGetLastError();
 	    if (err == WSAEWOULDBLOCK) {
@@ -1605,7 +1605,7 @@ void select_result(WPARAM wParam, LPARAM lParam)
 	 * end with type==2 (urgent data).
 	 */
 	ret = p_recv(s->s, buf, sizeof(buf), MSG_OOB);
-	noise_ultralight(ret);
+	noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 	if (ret <= 0) {
             int err = p_WSAGetLastError();
 	    plug_closing(s->plug, winsock_error_string(err), err, 0);
diff --git a/windows/winnoise.c b/windows/winnoise.c
index 39c2049a..0c73321e 100644
--- a/windows/winnoise.c
+++ b/windows/winnoise.c
@@ -122,26 +122,26 @@ void noise_regular(void)
     FILETIME times[4];
 
     w = GetForegroundWindow();
-    random_add_noise(&w, sizeof(w));
+    random_add_noise(NOISE_SOURCE_FGWINDOW, &w, sizeof(w));
     w = GetCapture();
-    random_add_noise(&w, sizeof(w));
+    random_add_noise(NOISE_SOURCE_CAPTURE, &w, sizeof(w));
     w = GetClipboardOwner();
-    random_add_noise(&w, sizeof(w));
+    random_add_noise(NOISE_SOURCE_CLIPBOARD, &w, sizeof(w));
     z = GetQueueStatus(QS_ALLEVENTS);
-    random_add_noise(&z, sizeof(z));
+    random_add_noise(NOISE_SOURCE_QUEUE, &z, sizeof(z));
 
     GetCursorPos(&pt);
-    random_add_noise(&pt, sizeof(pt));
+    random_add_noise(NOISE_SOURCE_CURSORPOS, &pt, sizeof(pt));
 
     GlobalMemoryStatus(&memstat);
-    random_add_noise(&memstat, sizeof(memstat));
+    random_add_noise(NOISE_SOURCE_MEMINFO, &memstat, sizeof(memstat));
 
     GetThreadTimes(GetCurrentThread(), times, times + 1, times + 2,
 		   times + 3);
-    random_add_noise(&times, sizeof(times));
+    random_add_noise(NOISE_SOURCE_THREADTIME, &times, sizeof(times));
     GetProcessTimes(GetCurrentProcess(), times, times + 1, times + 2,
 		    times + 3);
-    random_add_noise(&times, sizeof(times));
+    random_add_noise(NOISE_SOURCE_PROCTIME, &times, sizeof(times));
 }
 
 /*
@@ -150,16 +150,16 @@ void noise_regular(void)
  * counter to the noise pool. It gets the scan code or mouse
  * position passed in.
  */
-void noise_ultralight(unsigned long data)
+void noise_ultralight(NoiseSourceId id, unsigned long data)
 {
     DWORD wintime;
     LARGE_INTEGER perftime;
 
-    random_add_noise(&data, sizeof(DWORD));
+    random_add_noise(id, &data, sizeof(DWORD));
 
     wintime = GetTickCount();
-    random_add_noise(&wintime, sizeof(DWORD));
+    random_add_noise(NOISE_SOURCE_TIME, &wintime, sizeof(DWORD));
 
     if (QueryPerformanceCounter(&perftime))
-	random_add_noise(&perftime, sizeof(perftime));
+	random_add_noise(NOISE_SOURCE_PERFCOUNT, &perftime, sizeof(perftime));
 }
diff --git a/windows/winplink.c b/windows/winplink.c
index fa6f4c98..cbfdeaff 100644
--- a/windows/winplink.c
+++ b/windows/winplink.c
@@ -220,7 +220,7 @@ int stdin_gotdata(struct handle *h, void *data, int len)
 	fprintf(stderr, "Unable to read from standard input: %s\n", buf);
 	cleanup_exit(0);
     }
-    noise_ultralight(len);
+    noise_ultralight(NOISE_SOURCE_IOLEN, len);
     if (backend_connected(backend)) {
 	if (len > 0) {
             return backend_send(backend, data, len);
@@ -574,8 +574,7 @@ int main(int argc, char **argv)
                     };
                     int e;
 
-		    noise_ultralight(socket);
-		    noise_ultralight(things.lNetworkEvents);
+		    noise_ultralight(NOISE_SOURCE_IOID, socket);
 
                     for (e = 0; e < lenof(eventtypes); e++)
                         if (things.lNetworkEvents & eventtypes[e].mask) {
diff --git a/windows/winsftp.c b/windows/winsftp.c
index 27c03616..31683e5a 100644
--- a/windows/winsftp.c
+++ b/windows/winsftp.c
@@ -578,8 +578,7 @@ int do_eventsel_loop(HANDLE other_event)
 		};
 		int e;
 
-		noise_ultralight(socket);
-		noise_ultralight(things.lNetworkEvents);
+		noise_ultralight(NOISE_SOURCE_IOID, socket);
 
 		for (e = 0; e < lenof(eventtypes); e++)
 		    if (things.lNetworkEvents & eventtypes[e].mask) {