--- a/js/src/jsapi-tests/testPrintf.cpp
+++ b/js/src/jsapi-tests/testPrintf.cpp
@@ -3,16 +3,17 @@
  */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/SizePrintfMacros.h"
 
+#include <cfloat>
 #include <stdarg.h>
 
 #include "jsprf.h"
 
 #include "jsapi-tests/tests.h"
 
 static bool
 MOZ_FORMAT_PRINTF(2, 3)
@@ -56,16 +57,20 @@ BEGIN_TEST(testPrintf)
     CHECK(print_one("27270", "%" PRIuSIZE, (size_t) 27270));
     CHECK(print_one("hello", "he%so", "ll"));
     CHECK(print_one("(null)", "%s", zero()));
     CHECK(print_one("0", "%p", (char *) 0));
     CHECK(print_one("h", "%c", 'h'));
     CHECK(print_one("1.500000", "%f", 1.5f));
     CHECK(print_one("1.5", "%g", 1.5));
 
+    // Regression test for bug#1350097.  The bug was an assertion
+    // failure caused by printing a very long floating point value.
+    print_one("ignore", "%lf", DBL_MAX);
+
     CHECK(print_one("2727", "%" PRIu32, (uint32_t) 2727));
     CHECK(print_one("aa7", "%" PRIx32, (uint32_t) 2727));
     CHECK(print_one("2727", "%" PRIu64, (uint64_t) 2727));
     CHECK(print_one("aa7", "%" PRIx64, (uint64_t) 2727));
 
     return true;
 }
 END_TEST(testPrintf)

--- a/mozglue/misc/Printf.cpp
+++ b/mozglue/misc/Printf.cpp
@@ -250,17 +250,18 @@ mozilla::PrintfTarget::cvt_ll(int64_t nu
 /*
  * Convert a double precision floating point number into its printable
  * form.
  */
 bool
 mozilla::PrintfTarget::cvt_f(double d, const char* fmt0, const char* fmt1)
 {
     char fin[20];
-    char fout[300];
+    // The size is chosen such that we can print DBL_MAX.  See bug#1350097.
+    char fout[320];
     int amount = fmt1 - fmt0;
 
     MOZ_ASSERT((amount > 0) && (amount < (int)sizeof(fin)));
     if (amount >= (int)sizeof(fin)) {
         // Totally bogus % command to sprintf. Just ignore it
         return true;
     }
     memcpy(fin, fmt0, (size_t)amount);
@@ -272,17 +273,17 @@ mozilla::PrintfTarget::cvt_f(double d, c
         const char* p = fin;
         while (*p) {
             MOZ_ASSERT(*p != 'L');
             p++;
         }
     }
 #endif
     size_t len = SprintfLiteral(fout, fin, d);
-    MOZ_ASSERT(len <= sizeof(fout));
+    MOZ_RELEASE_ASSERT(len <= sizeof(fout));
 
     return emit(fout, len);
 }
 
 /*
  * Convert a string into its printable form.  "width" is the output
  * width. "prec" is the maximum number of characters of "s" to output,
  * where -1 means until NUL.