diff --git a/mozilla/nsprpub/pr/src/misc/prtime.c b/mozilla/nsprpub/pr/src/misc/prtime.c
index d73b08cdeae..5f05d5ef68e 100644
--- a/mozilla/nsprpub/pr/src/misc/prtime.c
+++ b/mozilla/nsprpub/pr/src/misc/prtime.c
@@ -1698,29 +1698,37 @@ PR_FormatTime(char *buf, int buflen, const char *fmt, const PRExplodedTime *tm)
 {
     size_t rv;
     struct tm a;
-    a.tm_sec = tm->tm_sec;
-    a.tm_min = tm->tm_min;
-    a.tm_hour = tm->tm_hour;
-    a.tm_mday = tm->tm_mday;
-    a.tm_mon = tm->tm_month;
-    a.tm_wday = tm->tm_wday;
-    a.tm_year = tm->tm_year - 1900;
-    a.tm_yday = tm->tm_yday;
-    a.tm_isdst = tm->tm_params.tp_dst_offset ? 1 : 0;
+    struct tm *ap;
 
-/*
- * On some platforms, for example SunOS 4, struct tm has two additional
- * fields: tm_zone and tm_gmtoff.
- */
+    if (tm) {
+        ap = &a;
+        a.tm_sec = tm->tm_sec;
+        a.tm_min = tm->tm_min;
+        a.tm_hour = tm->tm_hour;
+        a.tm_mday = tm->tm_mday;
+        a.tm_mon = tm->tm_month;
+        a.tm_wday = tm->tm_wday;
+        a.tm_year = tm->tm_year - 1900;
+        a.tm_yday = tm->tm_yday;
+        a.tm_isdst = tm->tm_params.tp_dst_offset ? 1 : 0;
+
+        /*
+         * On some platforms, for example SunOS 4, struct tm has two
+         * additional fields: tm_zone and tm_gmtoff.
+         */
 
 #if defined(SUNOS4) || (__GLIBC__ >= 2) || defined(XP_BEOS) \
         || defined(NETBSD) || defined(OPENBSD) || defined(FREEBSD) \
         || defined(DARWIN) || defined(SYMBIAN)
-    a.tm_zone = NULL;
-    a.tm_gmtoff = tm->tm_params.tp_gmt_offset + tm->tm_params.tp_dst_offset;
+        a.tm_zone = NULL;
+        a.tm_gmtoff = tm->tm_params.tp_gmt_offset +
+                      tm->tm_params.tp_dst_offset;
 #endif
+    } else {
+        ap = NULL;
+    }
 
-    rv = strftime(buf, buflen, fmt, &a);
+    rv = strftime(buf, buflen, fmt, ap);
     if (!rv && buf && buflen > 0) {
         /*
          * When strftime fails, the contents of buf are indeterminate.
diff --git a/mozilla/nsprpub/pr/tests/formattm.c b/mozilla/nsprpub/pr/tests/formattm.c
index c3c758b5f28..8b04cd3701e 100644
--- a/mozilla/nsprpub/pr/tests/formattm.c
+++ b/mozilla/nsprpub/pr/tests/formattm.c
@@ -44,16 +44,39 @@
 int main()
 {
     char buffer[256];
+    char small_buffer[8];
     PRTime now;
     PRExplodedTime tod;
 
     now = PR_Now();
     PR_ExplodeTime(now, PR_LocalTimeParameters, &tod);
-    (void)PR_FormatTime(buffer, sizeof(buffer),
-        "%a %b %d %H:%M:%S %Z %Y", &tod);
-    printf("%s\n", buffer);
+
+    if (PR_FormatTime(buffer, sizeof(buffer),
+            "%a %b %d %H:%M:%S %Z %Y", &tod) != 0) {
+        printf("%s\n", buffer);
+    } else {
+        fprintf(stderr, "PR_FormatTime(buffer) failed\n");
+        return 1;
+    }
+
+    small_buffer[0] = '?';
+    if (PR_FormatTime(small_buffer, sizeof(small_buffer),
+            "%a %b %d %H:%M:%S %Z %Y", &tod) == 0) {
+        if (small_buffer[0] != '\0') {
+            fprintf(stderr, "PR_FormatTime(small_buffer) did not output "
+                            "an empty string on failure\n");
+            return 1;
+        }
+        printf("%s\n", small_buffer);
+    } else {
+        fprintf(stderr, "PR_FormatTime(small_buffer) succeeded "
+                        "unexpectedly\n");
+        return 1;
+    }
+
     (void)PR_FormatTimeUSEnglish(buffer, sizeof(buffer),
         "%a %b %d %H:%M:%S %Z %Y", &tod);
     printf("%s\n", buffer);
+
     return 0;
 }